Add test for introspection as subscription root

Add a pending test checking that an introspection field cannot be
subscription root.

.ghci

@@ -1,2 +0,0 @@
-import Data.Attoparsec.Text
-import qualified Data.Text.IO as TIO

.gitea/deploy.awk

@@ -0,0 +1,3 @@
+END {
+    system("cabal upload --username belka --password "ENVIRON["HACKAGE_PASSWORD"]" "$0)
+}

.gitea/workflows/build.yml

@@ -0,0 +1,33 @@
+name: Build
+
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+    branches: [master]
+
+jobs:
+  audit:
+    runs-on: buildenv
+    steps:
+      - uses: actions/checkout@v4
+      - run: hlint -- src tests
+
+  test:
+    runs-on: buildenv
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install dependencies
+        run: cabal update
+      - name: Prepare system
+        run: cabal build graphql-test
+      - run: cabal test --test-show-details=streaming
+
+  doc:
+    runs-on: buildenv
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install dependencies
+        run: cabal update
+      - run: cabal haddock --enable-documentation

.gitea/workflows/release.yml

@@ -0,0 +1,17 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - '**'
+
+jobs:
+  release:
+    runs-on: buildenv
+    steps:
+      - uses: actions/checkout@v4
+      - name: Upload a candidate
+        env:
+          HACKAGE_PASSWORD: ${{ secrets.HACKAGE_PASSWORD }}
+        run: |
+          cabal sdist | awk -f .gitea/deploy.awk

.gitignore

@@ -1 +1,15 @@
+# Stack
 .stack-work/
+/stack.yaml.lock
+
+# Cabal
+/dist/
+/dist-newstyle/
+.cabal-sandbox/
+cabal.sandbox.config
+cabal.project.local
+
+# GHC
+*.hi
+*.o
+/docs/tutorial/tutorial

CHANGELOG.md

@@ -1,6 +1,534 @@
-# Change Log
+# Changelog
 All notable changes to this project will be documented in this file.
 
+The format is based on
+[Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to
+[Haskell Package Versioning Policy](https://pvp.haskell.org/).
+
+## [Unreleased]
+### Changed
+- Remove deprecated 'gql' quasi quoter.
+
+## [1.4.0.0] - 2024-10-26
+### Changed
+- `Schema.Directive` is extended to contain a boolean argument, representing
+  repeatable directives. The parser can parse repeatable directive definitions.
+  Validation allows repeatable directives.
+- `AST.Document.Directive` is a record.
+- `gql` quasi quoter is deprecated (moved to graphql-spice package).
+
+### Fixed
+- `gql` quasi quoter recognizeds all GraphQL line endings (CR, LF and CRLF).
+
+### Added
+- @specifiedBy directive.
+
+## [1.3.0.0] - 2024-05-01
+### Changed
+- Remove deprecated `runCollectErrs`, `Resolution`, `CollectErrsT` from the
+  `Error` module.
+
+## [1.2.0.3] - 2024-01-09
+### Fixed
+- Fix corrupted source distribution.
+
+## [1.2.0.2] - 2024-01-09
+### Fixed
+- `gql` removes not only leading `\n` but also `\r`.
+- Fix non nullable type string representation in executor error messages.
+- Fix input objects not being coerced to lists.
+- Fix used variables are not found in the properties of input objects.
+
+## [1.2.0.1] - 2023-04-25
+### Fixed
+- Support hspec 2.11.
+
+## [1.2.0.0] - 2023-02-28
+### Added
+- Schema printing.
+- `Semigroup` and `Monoid` instances for `AST.Document.Description`.
+- Support for vector 0.13.0.0 and transformers 0.6.1.0.
+
+### Fixed
+- Fix resolvers returning a list in the reverse order.
+
+### Removed
+- GHC 8 support.
+- Cabal -json flag.
+- `Test.Hspec.GraphQL`: moved to `graphql-spice` package.
+- CPP `ifdef WITH_JSON` blocks.
+
+## [1.1.0.0] - 2022-12-24
+### Changed
+- Removed deprecated `Language.GraphQL.Error` functions: `addErr`, `addErrMsg`,
+  `singleError`.
+- Deprecate `Resolution`, `CollectErrsT` and `runCollectErrs` in the `Error`
+  module. It was already noted in the documentation that these symbols are
+  deprecated, now a pragma is added.
+- `Language.GraphQL`: Added information about the *json* flag and switching to
+  *graphql-spice* for JSON support.
+
+### Added
+- Partial schema printing: operation type encoder.
+
+## [1.0.3.0] - 2022-03-27
+### Fixed
+- Index position in error path. (Index and Segment paths of a field have been
+  swapped).
+- Parsing empty list as an argument.
+
+### Added
+- quickCheck Parser test for arguments. Arbitrary instances for Language.GraphQL.AST.Document.
+- Enhanced query error messages. Add tests for these cases.
+- Allow version 2.0 of the text package.
+
+## [1.0.2.0] - 2021-12-26
+### Added
+- `Serialize` instance for `Type.Definition.Value`.
+- `VariableValue` instance for `Type.Definition.Value`.
+- `Json` build flag, enabled by default. JSON and Aeson support can be disabled
+  by disabling this flag.
+
+## [1.0.1.0] - 2021-09-27
+### Added
+- Custom `Show` instance for `Type.Definition.Value` (for error
+  messages).
+- Path information in errors (path to the field throwing the error).
+- Deprecation notes in the `Error` module for `Resolution`, `CollectErrsT` and
+  `runCollectErrs`. These symbols are part of the old executor and aren't used
+  anymore, it will be deprecated in the future and removed.
+- `TH` module with the `gql` quasi quoter.
+
+### Fixed
+- Error messages are more concrete, they also contain type information and
+  wrong values, where appropriate and possible.
+- If the field with an error is Non-Nullable, the error is propagated to the
+  first nullable field, as required by the specification.
+
+## [1.0.0.0] - 2021-07-04
+### Added
+- `Language.GraphQL.Execute.OrderedMap` is a map data structure, that preserves
+  insertion order.
+- `Language.GraphQL.Schema.schemaWithTypes` constructs a complete schema,
+  including an optional schema description and user-defined types not referenced
+  in the schema directly (for example interface implementations).
+- `Language.GraphQL.Schema.description` returns the optional schema description.
+- All errors that can be associated with a location in the query contain
+  location information.
+
+### Fixed
+- Parser now accepts empty lists and objects.
+- Parser now accepts all directive locations.
+- `valuesOfCorrectTypeRule` doesn't check lists recursively since the
+  validation traverser calls it on all list items.
+- `valuesOfCorrectTypeRule` doesn't check objects recursively since the
+  validation traverser calls it on all object properties.
+- Validation of non-nullable values inside lists.
+- `executeField` shouldn't assume that a selection has only one field with a
+  given name, but it should take the first field. The underlying cause is a
+  wrong pattern, which (because of the laziness) is executed only if the field
+  has arguments.
+
+### Changed
+- `AST.Document.Value.List` and `AST.Document.ConstValue.ConstList` contain
+  location information for each list item.
+- `Error`: `singleError`, `addErr` and `addErrMsg` are deprecated. They are
+  internal functions used by the executor for error handling.
+
+## [0.11.1.0] - 2021-02-07
+### Added
+- `Validate.Rules`:
+  - `overlappingFieldsCanBeMergedRule`
+  - `possibleFragmentSpreadsRule`
+  - `variablesInAllowedPositionRule`
+  - `valuesOfCorrectTypeRule`
+- `Type.Schema.implementations` contains a map from interfaces and objects to
+  interfaces they implement.
+- Show instances for GraphQL type definitions in the `Type` modules.
+- Custom Show instances for type and value representations in the AST.
+- `AST.Document.escape` escapes a single character in a `StringValue`.
+
+## [0.11.0.0] - 2020-11-07
+### Changed
+- `AST.Document.Selection` wraps additional new types: `Field`, `FragmentSpread`
+  and  `InlineFragment`. Thus validation rules can be defined more concise.
+- `AST.Document`: `Argument` and `Directive` contain token location.
+- `AST.Document.Argument` contains the `Value` wrapped in the `Node`.
+- `AST.Lexer.colon` and `AST.Lexer.at` ignore the result (it is always the
+- same).
+- `Validate.Validation`: `Validation.rules` was removed. `Validation.rules`
+  contained the list of rules, but the executed rules shouldn't know about other
+  rules. `rules` was a part of the `Validation` context to pass it easier
+  around, but since the rules are traversed once now and applied to all nodes in
+  the tree at the beginning, it isn't required anymore.
+- `Validate.Validation.Error`: `path` is removed since it isn't possible to get
+  the path without executing the query.
+- `Error.Error`: `path` added. It is currently always empty.
+- `Validate.Validation.Path` was moved to `Error`.
+- `Type.Schema.Schema`: data constructor is hidden, fields are accessible with
+  freestanding functions: `query`, `mutation`, `subscription`, `directives` and
+  `types`.
+
+### Added
+- `Validate.Validation.Rule` constructors:
+  - `SelectionRule`
+  - `FragmentRule`
+  - `FragmentSpreadRule`
+  - `ArgumentsRule`
+  - `DirectivesRule`
+  - `VariablesRule`
+  - `FieldRule`
+- `Validate.Rules`:
+  - `fragmentsOnCompositeTypesRule`
+  - `fragmentSpreadTargetDefinedRule`
+  - `fragmentSpreadTypeExistenceRule`
+  - `noUnusedFragmentsRule`
+  - `noFragmentCyclesRule`
+  - `uniqueArgumentNamesRule`
+  - `uniqueDirectiveNamesRule`
+  - `uniqueVariableNamesRule`
+  - `variablesAreInputTypesRule`
+  - `noUndefinedVariablesRule`
+  - `noUndefinedVariablesRule`
+  - `noUnusedVariablesRule`
+  - `uniqueInputFieldNamesRule`
+  - `fieldsOnCorrectTypeRule`
+  - `scalarLeafsRule`
+  - `knownArgumentNamesRule`
+  - `knownDirectiveNamesRule`
+  - `directivesInValidLocationsRule`
+  - `providedRequiredArgumentsRule`
+  - `providedRequiredInputFieldsRule`
+- `AST.Document.Field`.
+- `AST.Document.FragmentSpread`.
+- `AST.Document.InlineFragment`.
+- `AST.Document.Node`.
+- `Type.In.Arguments`: Type alias for an argument map.
+- `Type.Schema.Directive` and `Type.Schema.Directives` are directive definition
+  representation.
+- `Type.Schema.schema`: Schema constructor.
+
+### Fixed
+- Collecting existing types from the schema considers subscriptions.
+
+### Removed
+- `AST.Document.Alias`. Use `AST.Document.Name` instead.
+
+## [0.10.0.0] - 2020-08-29
+### Changed
+- `Test.Hspec.GraphQL.*`: replace `IO` in the resolver with any `MonadCatch`.
+- The `Location` argument of `AST.Document.Definition.ExecutableDefinition` was
+  moved to `OperationDefinition` and `FragmentDefinition` since these are the
+  actual elements that have a location in the document.
+- `Validate.Rules` get the whole validation context (AST and schema).
+
+### Added
+- `Validate.Validation` contains data structures and functions used by the
+  validator and concretet rules.
+- `Validate.Rules`: operation validation rules.
+
+## [0.9.0.0] - 2020-07-24
+### Fixed
+- Location of a parse error is returned in a singleton array with key
+  `locations`.
+- Parsing comments in the front of definitions.
+- Some missing labels were added to the parsers, some labels were fixed to
+  refer to the AST nodes being parsed.
+
+### Added
+- `AST` reexports `AST.Parser`.
+- `AST.Document.Location` is a token location as a line and column pair.
+- `Execute` reexports `Execute.Coerce`.
+- `Error.Error` is an error representation with a message and source location.
+- `Error.Response` represents a result of running a GraphQL query.
+- `Type.Schema` exports `Type` which lists all types possible in the schema.
+- Parsing subscriptions.
+- `Error.ResponseEventStream`, `Type.Out.Resolve`, `Type.Out.Subscribe` and
+  `Type.Out.SourceEventStream` define subscription resolvers.
+- `Error.ResolverException` is an exception that can be thrown by (field value
+  and event stream) resolvers to signalize an error. Other exceptions will
+  escape.
+- `Test.Hspec.GraphQL` contains some test helpers.
+- `Validate` contains the validator and standard rules.
+
+### Changed
+- `Type.Out.Resolver`: Interface fields don't have resolvers, object fields
+  have value resolvers, root subscription type resolvers need an additional
+  resolver that creates an event stream. `Resolver` represents these differences
+  now and pairs a field with the function(s). Resolvers don't have `ExceptT`,
+  errors are handled with `MonadThrow`/`MonadCatch`.
+- All code from `Trans` is moved to `Type.Out` and exported by `Type` and
+  `Type.Out`.
+- `AST.Core` contained only `Arguments` which was moved to `Type.Definition`.
+  `AST` provides now only functionality related to parsing and encoding, as it
+  should be.
+- `Execute.execute` takes an additional argument, a possible operation name
+  and returns either a stream or the response.
+- `Error` module was changed to work with dedicated types for errors and the
+  response instead of JSON.
+- `graphqlSubs` takes an additional argument, the operation name. The type of
+  variable names is changed back to JSON since it is a common format and it
+  saves additional conversions. Custom format still can be used with the
+  underlying functions (in the `Execute` module). The function returns either a
+  a stream or the resolved value.
+- `graphql` returns either a stream or the resolved value.
+- The constraint of the base monad was changed to `MonadCatch` (and it implies
+  `MonadThrow`).
+
+### Removed
+- `Trans.ActionT` is an unneeded layer of complexity. `Type.Out.Resolver`
+  represents possible resolver configurations.
+- `Execute.executeWithName`. `Execute.execute` takes the operation name and
+   completely replaces `executeWithName`.
+
+## [0.8.0.0] - 2020-06-20
+### Fixed
+- The parser rejects variables when parsing defaultValue (DefaultValue). The
+  specification defines default values as `Value` with `const` parameter and
+  constants cannot be variables. `AST.Document.ConstValue` was added,
+  `AST.Document.ObjectField` was modified.
+- AST transformation should never fail.
+    * Arguments and fields with a missing variable as value should be left out.
+    * Invalid (recusrive or non-existing) fragments should be skipped.
+- Argument value coercion.
+- Variable value coercion.
+- Result coercion.
+- The executor should skip the fields missing in the object type and not fail.
+- Merging subselections.
+
+### Changed
+- `Schema.Resolver` was moved to `Type.Out`, it is a field and resolver function
+  pair.
+- `AST.Core.Value` was moved into `Type.Definition`. These values are used only
+  in the execution and type system, it is not a part of the parsing tree.
+- `Type` module is superseded by `Type.Out`. This module contains now only
+  exports from other module that complete `Type.In` and `Type.Out` exports.
+- `Error.CollectErrsT` contains the new `Resolution` data structure.
+  `Resolution` represents the state used by the executor. It contains all types
+  defined in the schema and collects the thrown errors.
+
+### Added
+- `Type.Definition` contains base type system definition, e.g. Enums and
+  Scalars.
+- `Type.Schema` describes a schema. Both public functions that execute queries
+  accept a `Schema` now instead of a `HashMap`. The execution fails if the root
+  operation doesn't match the root Query type in the schema.
+- `Type.In` and `Type.Out` contain definitions for input and output types.
+- `Execute.Coerce` defines a typeclass responsible for input, variable value
+  coercion. It decouples us a bit from JSON since any format can be used to pass
+  query variables. Execution functions accept (`HashMap Name a`) instead of
+  `Subs`, where a is an instance of `VariableValue`.
+
+### Removed
+- `Schema.scalar`, `Schema.wrappedScalar`. They accepted everything can be
+  converted to JSON and JSON is not suitable as an internal representation for
+  GraphQL. E.g. GraphQL distinguishes between Floats and Integers.
+- `Schema.wrappedObject`, `Schema.object`, `Schema.resolversToMap`. There is no
+  need in special functions to construct field resolvers anymore, resolvers are
+  normal functions attached to the fields in the schema representation.
+- `Schema.resolve` is superseded by `Execute.Execution`.
+- `Error.runAppendErrs` isn't used anywhere.
+- `AST.Core`: `Document`, `Directive`, `Field`, `Fragment`, `Selection`, `Alias`
+  `TypeCondition` were modified, moved into `Execute.Transform.Document` and
+  made private. These types describe intermediate representation used by the
+  executor internally. Moving was required to avoid cyclic dependencies between
+  the executor and type system.
+- `AST.Core` doesn't reexports anything.
+
+## [0.7.0.0] - 2020-05-11
+### Fixed
+- Result of null encoding
+- Block strings encoding
+- Result of tab and newline encoding
+
+### Added
+- AST for the GraphQL schema.
+- Type system definition parser.
+- `Trans.argument`.
+- Schema extension parser.
+- Contributing guidelines.
+- `Schema.resolversToMap` (intended to be used internally).
+
+### Changed
+- Rename `AST.Definition` into `AST.Document.ExecutableDefinition`.
+  `AST.Document.TypeSystemDefinition` and `AST.Document.TypeSystemExtension`
+  can also be definitions.
+- Move all AST data to `AST.Document` and reexport them.
+- Rename `AST.OperationSelectionSet` to `AST.Document.SelectionSet`.
+- Make `Schema.Subs` a `Data.HashMap.Strict` (was a function
+  `key -> Maybe value` before).
+- Make `AST.Lexer.at` a text (symbol) parser. It was a char before and is
+  `symbol "@"` now.
+- Replace `MonadIO` with a plain `Monad`. Since the tests don't use IO,
+  set the inner monad to `Identity`.
+- `NonEmpty (Resolver m)` is now `HashMap Text (NonEmpty (Resolver m))`. Root
+  operation type can be any type, therefore a hashmap is needed. Since types
+  cannot be empty, we save the list of resolvers in the type as a non-empty
+  list. Currently only "Query" and "Mutation" are supported as types. For more
+  schema support is required. The executor checks now if the type in the query
+  matches the type of the provided root resolvers.
+
+### Removed
+- `AST.Field`, `AST.InlineFragment` and `AST.FragmentSpread`.
+  These types are only used in `AST.Selection` and `AST.Selection` contains now
+  3 corresponding data constructors, `Field`, `InlineFragment` and
+  `FragmentSpread`, instead of separate types. It simplifies pattern matching
+  and doesn't make the code less typesafe.
+- `Schema.scalarA`.
+- `Schema.wrappedScalarA`.
+- `Schema.wrappedObjectA`.
+- `Schema.objectA`.
+- `AST.Argument`. Replaced with `AST.Arguments` which holds all arguments as a
+  key/value map.
+
+## [0.6.1.0] - 2019-12-23
+### Fixed
+- Parsing multiple string arguments, such as
+  `login(username: "username", password: "password")` would fail on the comma
+  due to strings not having a space consumer.
+- Fragment spread is evaluated based on the `__typename` resolver. If the
+  resolver is missing, it is assumed that the type condition is satisfied (all
+  fragments are included).
+- Escaping characters during encoding.
+
+### Added
+- Directive support (@skip and @include).
+- Pretifying multi-line string arguments as block strings.
+
+## [0.6.0.0] - 2019-11-27
+### Changed
+- `Language.GraphQL.Encoder` moved to `Language.GraphQL.AST.Encoder`.
+- `Language.GraphQL.Parser` moved to `Language.GraphQL.AST.Parser`.
+- `Language.GraphQL.Lexer` moved to `Language.GraphQL.AST.Lexer`.
+- All `Language.GraphQL.AST.Value` data constructor prefixes were removed. The
+  module should be imported qualified.
+- All `Language.GraphQL.AST.Core.Value` data constructor prefixes were removed.
+  The module should be imported qualified.
+- `Language.GraphQL.AST.Core.Object` is now just a HashMap.
+- `Language.GraphQL.AST.Transform` is isn't exposed publically anymore.
+- `Language.GraphQL.Schema.resolve` accepts a selection `Seq` (`Data.Sequence`)
+  instead of a list. Selections are stored as sequences internally as well.
+- Add a reader instance to the resolver's monad stack. The Reader contains
+  a Name/Value hashmap, which will contain resolver arguments.
+
+### Added
+- Nested fragment support.
+
+### Fixed
+- Consume ignored tokens after `$` and `!`. I mistakenly assumed that
+  `$variable` is a single token, same as `Type!` is a single token. This is not
+  the case, for example `Variable` is defined as `$ Name`, so these are two
+  tokens, therefore whitespaces and commas after `$` and `!` should be
+  consumed.
+
+### Improved
+- `Language.GraphQL.AST.Parser.type_`: Try type parsers in a variable
+  definition in a different order to avoid using `but`.
+
+### Removed
+- `Language.GraphQL.AST.Arguments`. Use `[Language.GraphQL.AST.Argument]`
+  instead.
+- `Language.GraphQL.AST.Directives`. Use `[Language.GraphQL.AST.Directives]`
+  instead.
+- `Language.GraphQL.AST.VariableDefinitions`. Use
+  `[Language.GraphQL.AST.VariableDefinition]` instead.
+- `Language.GraphQL.AST.FragmentName`. Use `Language.GraphQL.AST.Name` instead.
+- `Language.GraphQL.Execute.Schema` - It was a resolver list, not a schema.
+- `Language.GraphQL.Schema`: `enum`, `enumA`, `wrappedEnum` and `wrappedEnumA`.
+  Use `scalar`, `scalarA`, `wrappedScalar` and `wrappedScalarA` instead.
+
+## [0.5.1.0] - 2019-10-22
+### Deprecated
+- `Language.GraphQL.AST.Arguments`. Use `[Language.GraphQL.AST.Argument]`
+  instead.
+- `Language.GraphQL.AST.Directives`. Use `[Language.GraphQL.AST.Directives]`
+  instead.
+- `Language.GraphQL.AST.VariableDefinitions`. Use
+  `[Language.GraphQL.AST.VariableDefinition]` instead.
+
+### Added
+- Module documentation.
+- Inline fragment support.
+
+### Fixed
+- Top-level fragments.
+- Fragment for execution is chosen based on the type.
+
+## [0.5.0.1] - 2019-09-10
+### Added
+- Minimal documentation for all public symbols.
+
+### Deprecated
+- `Language.GraphQL.AST.FragmentName`. Replaced with Language.GraphQL.AST.Name.
+- `Language.GraphQL.Execute.Schema` - It is not a schema (at least not a
+  complete one), but a resolver list, and the resolvers should be provided by
+  the user separately, because the schema can originate from a GraphQL
+  document. `Schema` name should be free to provide a data type for the real
+  schema later.
+- `Language.GraphQL.Schema`: `enum`, `enumA`, `wrappedEnum` and `wrappedEnumA`.
+  There are actually only two generic types in GraphQL: Scalars and objects.
+  Enum is a scalar value.
+
+### Fixed
+- Parsing block string values.
+
+## [0.5.0.0] - 2019-08-14
+### Added
+- `executeWithName` executes an operation with the given name.
+- Export `Language.GraphQL.Encoder.definition`,
+  `Language.GraphQL.Encoder.type'` and `Language.GraphQL.Encoder.directive`.
+- Export `Language.GraphQL.Encoder.value`. Escapes \ and " in strings now.
+
+### Changed
+- `Operation` includes now possible operation name which allows to support
+  documents with multiple operations.
+- `Language.GraphQL.Encoder.document` and other encoding functions take a
+  `Formatter` as argument to distinguish between minified and pretty printing.
+- All encoder functions return `Data.Text.Lazy`.
+
+### Removed
+- Unused `Language.GraphQL.Encoder.spaced`.
+
+## [0.4.0.0] - 2019-07-23
+### Added
+- Support for mutations.
+- Error handling (with monad transformers).
+- Nullable types.
+- Arbitrary nested lists support.
+- Potential BOM header parsing.
+
+### Changed
+- attoparsec is replaced with megaparsec.
+- The library is now under `Language.GraphQL` (instead of `Data.GraphQL`).
+- HUnit and tasty are replaced with Hspec.
+- `Alternative`/`MonadPlus` resolver constraints are replaced with `MonadIO`.
+
+### Removed
+- Duplicates from `Language.GraphQL.AST` already available in
+  `Language.GraphQL.AST.Core`.
+- All module exports are now explicit, so private and help functions aren't
+  exported anymore.
+
+## [0.3] - 2015-09-22
+### Changed
+- Exact match numeric types to spec.
+- Names follow now the spec.
+- AST slightly different for better readability or easier parsing.
+- Replace golden test for test to validate parsing/encoding.
+
+### Added
+- Parsing errors in all cases where `Alternative` is used.
+- GraphQL encoder.
+
+### Fixed
+- Expect braces `inputValueDefinitions` instead of parens when parsing.
+
+## [0.2.1] - 2015-09-16
+### Fixed
+- Include data files for golden tests in Cabal package.
+- Support for ghc-7.8.
+
 ## [0.2] - 2015-09-14
 ### Added
 - Rudimentary parser for `GraphQL` which successfully parses the sample file
@@ -10,6 +538,34 @@ All notable changes to this project will be documented in this file.
 - Many optional data types in `GraphQl` didn't need to be wrapped in a `Maybe`.
 - Some `newtype`s became type synonyms for easier parsing.
 
-## [0.1] - 2015-09-12
+## 0.1 - 2015-09-12
 ### Added
 - Data types for the GraphQL language.
+
+[Unreleased]: https://git.caraus.tech/OSS/graphql/compare/v1.4.0.0...master
+[1.4.0.0]: https://git.caraus.tech/OSS/graphql/compare/v1.3.0.0...v1.4.0.0
+[1.3.0.0]: https://git.caraus.tech/OSS/graphql/compare/v1.2.0.3...v1.3.0.0
+[1.2.0.3]: https://git.caraus.tech/OSS/graphql/compare/v1.2.0.2...v1.2.0.3
+[1.2.0.2]: https://git.caraus.tech/OSS/graphql/compare/v1.2.0.1...v1.2.0.2
+[1.2.0.1]: https://git.caraus.tech/OSS/graphql/compare/v1.2.0.0...v1.2.0.1
+[1.2.0.0]: https://git.caraus.tech/OSS/graphql/compare/v1.1.0.0...v1.2.0.0
+[1.1.0.0]: https://git.caraus.tech/OSS/graphql/compare/v1.0.3.0...v1.1.0.0
+[1.0.3.0]: https://git.caraus.tech/OSS/graphql/compare/v1.0.2.0...v1.0.3.0
+[1.0.2.0]: https://git.caraus.tech/OSS/graphql/compare/v1.0.1.0...v1.0.2.0
+[1.0.1.0]: https://git.caraus.tech/OSS/graphql/compare/v1.0.0.0...v1.0.1.0
+[1.0.0.0]: https://git.caraus.tech/OSS/graphql/compare/v0.11.1.0...v1.0.0.0
+[0.11.1.0]: https://git.caraus.tech/OSS/graphql/compare/v0.11.0.0...v0.11.1.0
+[0.11.0.0]: https://git.caraus.tech/OSS/graphql/compare/v0.10.0.0...v0.11.0.0
+[0.10.0.0]: https://git.caraus.tech/OSS/graphql/compare/v0.9.0.0...v0.10.0.0
+[0.9.0.0]: https://git.caraus.tech/OSS/graphql/compare/v0.8.0.0...v0.9.0.0
+[0.8.0.0]: https://git.caraus.tech/OSS/graphql/compare/v0.7.0.0...v0.8.0.0
+[0.7.0.0]: https://git.caraus.tech/OSS/graphql/compare/v0.6.1.0...v0.7.0.0
+[0.6.1.0]: https://git.caraus.tech/OSS/graphql/compare/v0.6.0.0...v0.6.1.0
+[0.6.0.0]: https://git.caraus.tech/OSS/graphql/compare/v0.5.1.0...v0.6.0.0
+[0.5.1.0]: https://git.caraus.tech/OSS/graphql/compare/v0.5.0.1...v0.5.1.0
+[0.5.0.1]: https://git.caraus.tech/OSS/graphql/compare/v0.5.0.0...v0.5.0.1
+[0.5.0.0]: https://git.caraus.tech/OSS/graphql/compare/v0.4.0.0...v0.5.0.0
+[0.4.0.0]: https://git.caraus.tech/OSS/graphql/compare/v0.3...v0.4.0.0
+[0.3]: https://git.caraus.tech/OSS/graphql/compare/v0.2.1...v0.3
+[0.2.1]: https://git.caraus.tech/OSS/graphql/compare/v0.2...v0.2.1
+[0.2]: https://git.caraus.tech/OSS/graphql/compare/v0.1...v0.2

Data/GraphQL/AST.hs

@@ -1,143 +0,0 @@
-module Data.GraphQL.AST where
-
-import Data.Text (Text)
-
--- * Name
-
-type Name = Text
-
--- * Document
-
-newtype Document = Document [Definition] deriving (Eq,Show)
-
-data Definition = DefinitionOperation OperationDefinition
-                | DefinitionFragment  FragmentDefinition
-                | DefinitionType      TypeDefinition
-                  deriving (Eq,Show)
-
-data OperationDefinition =
-    Query        Name [VariableDefinition] [Directive] SelectionSet
-  | Mutation     Name [VariableDefinition] [Directive] SelectionSet
-  -- Not official yet
-  -- -- | Subscription Name [VariableDefinition] [Directive] SelectionSet
-    deriving (Eq,Show)
-
-data VariableDefinition = VariableDefinition Variable Type (Maybe DefaultValue)
-                          deriving (Eq,Show)
-
-newtype Variable = Variable Name deriving (Eq,Show)
-
-type SelectionSet = [Selection]
-
-data Selection = SelectionField Field
-               | SelectionFragmentSpread FragmentSpread
-               | SelectionInlineFragment InlineFragment
-                 deriving (Eq,Show)
-
-data Field = Field Alias Name [Argument]
-                              [Directive]
-                              SelectionSet
-             deriving (Eq,Show)
-
-type Alias = Name
-
-data Argument = Argument Name Value deriving (Eq,Show)
-
--- * Fragments
-
-data FragmentSpread = FragmentSpread Name [Directive]
-                      deriving (Eq,Show)
-
-data InlineFragment =
-    InlineFragment TypeCondition [Directive] SelectionSet
-    deriving (Eq,Show)
-
-data FragmentDefinition =
-    FragmentDefinition Name TypeCondition [Directive] SelectionSet
-    deriving (Eq,Show)
-
-type TypeCondition = NamedType
-
--- * Values
-
-data Value = ValueVariable Variable
-           | ValueInt Int -- TODO: Should this be `Integer`?
-           | ValueFloat Double -- TODO: Should this be `Scientific`?
-           | ValueBoolean Bool
-           | ValueString Text
-           | ValueEnum Name
-           | ValueList ListValue
-           | ValueObject ObjectValue
-             deriving (Eq,Show)
-
-newtype ListValue = ListValue [Value] deriving (Eq,Show)
-
-newtype ObjectValue = ObjectValue [ObjectField] deriving (Eq,Show)
-
-data ObjectField = ObjectField Name Value deriving (Eq,Show)
-
-type DefaultValue = Value
-
--- * Directives
-
-data Directive = Directive Name [Argument] deriving (Eq,Show)
-
--- * Type Reference
-
-data Type = TypeNamed NamedType
-          | TypeList ListType
-          | TypeNonNull NonNullType
-            deriving (Eq,Show)
-
-newtype NamedType = NamedType Name deriving (Eq,Show)
-
-newtype ListType = ListType Type deriving (Eq,Show)
-
-data NonNullType = NonNullTypeNamed NamedType
-                 | NonNullTypeList  ListType
-                   deriving (Eq,Show)
-
--- * Type definition
-
-data TypeDefinition = TypeDefinitionObject        ObjectTypeDefinition
-                    | TypeDefinitionInterface     InterfaceTypeDefinition
-                    | TypeDefinitionUnion         UnionTypeDefinition
-                    | TypeDefinitionScalar        ScalarTypeDefinition
-                    | TypeDefinitionEnum          EnumTypeDefinition
-                    | TypeDefinitionInputObject   InputObjectTypeDefinition
-                    | TypeDefinitionTypeExtension TypeExtensionDefinition
-                      deriving (Eq,Show)
-
-data ObjectTypeDefinition = ObjectTypeDefinition Name Interfaces [FieldDefinition]
-                            deriving (Eq,Show)
-
-type Interfaces = [NamedType]
-
-data FieldDefinition = FieldDefinition Name ArgumentsDefinition Type
-                       deriving (Eq,Show)
-
-type ArgumentsDefinition = [InputValueDefinition]
-
-data InputValueDefinition = InputValueDefinition Name Type (Maybe DefaultValue)
-                            deriving (Eq,Show)
-
-data InterfaceTypeDefinition = InterfaceTypeDefinition Name [FieldDefinition]
-                               deriving (Eq,Show)
-
-data UnionTypeDefinition = UnionTypeDefinition Name [NamedType]
-                           deriving (Eq,Show)
-
-data ScalarTypeDefinition = ScalarTypeDefinition Name
-                            deriving (Eq,Show)
-
-data EnumTypeDefinition = EnumTypeDefinition Name [EnumValueDefinition]
-                          deriving (Eq,Show)
-
-newtype EnumValueDefinition = EnumValueDefinition Name
-                              deriving (Eq,Show)
-
-data InputObjectTypeDefinition = InputObjectTypeDefinition Name [InputValueDefinition]
-                                 deriving (Eq,Show)
-
-newtype TypeExtensionDefinition = TypeExtensionDefinition ObjectTypeDefinition
-                                  deriving (Eq,Show)

Data/GraphQL/Parser.hs

@@ -1,322 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE LambdaCase #-}
-module Data.GraphQL.Parser where
-
-import Prelude hiding (takeWhile)
-import Control.Applicative ((<|>), empty, many, optional)
-import Control.Monad (when)
-import Data.Char
-
-import Data.Text (Text, pack)
-import Data.Attoparsec.Text
-  ( Parser
-  , (<?>)
-  , anyChar
-  , decimal
-  , double
-  , endOfLine
-  , many1
-  , manyTill
-  , option
-  , peekChar
-  , satisfy
-  , sepBy1
-  , signed
-  )
-
-import Data.GraphQL.AST
-
--- * Name
-
--- XXX: Handle starting `_` and no number at the beginning:
--- https://facebook.github.io/graphql/#sec-Names
--- TODO: Use takeWhile1 instead for efficiency. With takeWhile1 there is no
--- parsing failure.
-name :: Parser Name
-name = tok $ pack <$> many1 (satisfy isAlphaNum)
-
--- * Document
-
-document :: Parser Document
-document = whiteSpace
-     *> (Document <$> many1 definition)
-    -- Try SelectionSet when no definition
-    <|> (Document . pure
-                  . DefinitionOperation
-                  . Query mempty empty empty
-                <$> selectionSet)
-    <?> "document error!"
-
-definition :: Parser Definition
-definition = DefinitionOperation <$> operationDefinition
-         <|> DefinitionFragment  <$> fragmentDefinition
-         <|> DefinitionType      <$> typeDefinition
-         <?> "definition error!"
-
-operationDefinition :: Parser OperationDefinition
-operationDefinition =
-        op Query "query"
-    <|> op Mutation "mutation"
-    <?> "operationDefinition error!"
-  where
-    op f n = f <$ tok n <*> tok name
-                        <*> optempty variableDefinitions
-                        <*> optempty directives
-                        <*> selectionSet
-
-variableDefinitions :: Parser [VariableDefinition]
-variableDefinitions = parens (many1 variableDefinition)
-
-variableDefinition :: Parser VariableDefinition
-variableDefinition =
-    VariableDefinition <$> variable
-                       <*  tok ":"
-                       <*> type_
-                       <*> optional defaultValue
-
-defaultValue :: Parser DefaultValue
-defaultValue = tok "=" *> value
-
-variable :: Parser Variable
-variable = Variable <$ tok "$" <*> name
-
-selectionSet :: Parser SelectionSet
-selectionSet = braces $ many1 selection
-
-selection :: Parser Selection
-selection = SelectionField <$> field
-            -- Inline first to catch `on` case
-        <|> SelectionInlineFragment <$> inlineFragment
-        <|> SelectionFragmentSpread <$> fragmentSpread
-        <?> "selection error!"
-
-field :: Parser Field
-field = Field <$> optempty alias
-              <*> name
-              <*> optempty arguments
-              <*> optempty directives
-              <*> optempty selectionSet
-
-alias :: Parser Alias
-alias = name <* tok ":"
-
-arguments :: Parser [Argument]
-arguments = parens $ many1 argument
-
-argument :: Parser Argument
-argument = Argument <$> name <* tok ":" <*> value
-
--- * Fragments
-
-fragmentSpread :: Parser FragmentSpread
--- TODO: Make sure it fails when `... on`.
--- See https://facebook.github.io/graphql/#FragmentSpread
-fragmentSpread = FragmentSpread
-    <$  tok "..."
-    <*> name
-    <*> optempty directives
-
--- InlineFragment tried first in order to guard against 'on' keyword
-inlineFragment :: Parser InlineFragment
-inlineFragment = InlineFragment
-    <$  tok "..."
-    <*  tok "on"
-    <*> typeCondition
-    <*> optempty directives
-    <*> selectionSet
-
-fragmentDefinition :: Parser FragmentDefinition
-fragmentDefinition = FragmentDefinition
-    <$  tok "fragment"
-    <*> name
-    <*  tok "on"
-    <*> typeCondition
-    <*> optempty directives
-    <*> selectionSet
-
-typeCondition :: Parser TypeCondition
-typeCondition = namedType
-
--- * Values
-
--- This will try to pick the first type it can parse. If you are working with
--- explicit types use the `typedValue` parser.
-value :: Parser Value
-value = ValueVariable <$> variable
-        -- TODO: Handle arbitrary precision.
-    <|> ValueInt     <$> tok (signed decimal)
-    <|> ValueFloat   <$> tok (signed double)
-    <|> ValueBoolean <$> bool
-    -- TODO: Handle escape characters, unicode, etc
-    <|> ValueString  <$> quotes name
-    -- `true` and `false` have been tried before
-    <|> ValueEnum    <$> name
-    <|> ValueList    <$> listValue
-    <|> ValueObject  <$> objectValue
-
--- Notice it can be empty
-listValue :: Parser ListValue
-listValue = ListValue <$> brackets (many value)
-
--- Notice it can be empty
-objectValue :: Parser ObjectValue
-objectValue = ObjectValue <$> braces (many objectField)
-
-objectField :: Parser ObjectField
-objectField = ObjectField <$> name <* tok ":" <*> value
-
-bool :: Parser Bool
-bool = True  <$ tok "true"
-   <|> False <$ tok "false"
-
--- * Directives
-
-directives :: Parser [Directive]
-directives = many1 directive
-
-directive :: Parser Directive
-directive = Directive
-    <$  tok "@"
-    <*> name
-    <*> optempty arguments
-
--- * Type Reference
-
-type_ :: Parser Type
-type_ = TypeNamed   <$> namedType
-    <|> TypeList    <$> listType
-    <|> TypeNonNull <$> nonNullType
-
-namedType :: Parser NamedType
-namedType = NamedType <$> name
-
-listType :: Parser ListType
-listType = ListType <$> brackets type_
-
-nonNullType :: Parser NonNullType
-nonNullType = NonNullTypeNamed <$> namedType <* tok "!"
-          <|> NonNullTypeList  <$> listType  <* tok "!"
-
--- * Type Definition
-
-typeDefinition :: Parser TypeDefinition
-typeDefinition =
-        TypeDefinitionObject        <$> objectTypeDefinition
-    <|> TypeDefinitionInterface     <$> interfaceTypeDefinition
-    <|> TypeDefinitionUnion         <$> unionTypeDefinition
-    <|> TypeDefinitionScalar        <$> scalarTypeDefinition
-    <|> TypeDefinitionEnum          <$> enumTypeDefinition
-    <|> TypeDefinitionInputObject   <$> inputObjectTypeDefinition
-    <|> TypeDefinitionTypeExtension <$> typeExtensionDefinition
-    <?> "typeDefinition error!"
-
-objectTypeDefinition :: Parser ObjectTypeDefinition
-objectTypeDefinition = ObjectTypeDefinition
-    <$  tok "type"
-    <*> name
-    <*> optempty interfaces
-    <*> fieldDefinitions
-    <?> "objectTypeDefinition error!"
-
-interfaces :: Parser Interfaces
-interfaces = tok "implements" *> many1 namedType
-
-fieldDefinitions :: Parser [FieldDefinition]
-fieldDefinitions = braces $ many1 fieldDefinition
-
-fieldDefinition :: Parser FieldDefinition
-fieldDefinition = FieldDefinition
-    <$> name
-    <*> optempty argumentsDefinition
-    <*  tok ":"
-    <*> type_
-
-argumentsDefinition :: Parser ArgumentsDefinition
-argumentsDefinition = inputValueDefinitions
-
-inputValueDefinitions :: Parser [InputValueDefinition]
-inputValueDefinitions = parens $ many1 inputValueDefinition
-
-inputValueDefinition :: Parser InputValueDefinition
-inputValueDefinition = InputValueDefinition
-    <$> name
-    <*  tok ":"
-    <*> type_
-    <*> optional defaultValue
-
-interfaceTypeDefinition :: Parser InterfaceTypeDefinition
-interfaceTypeDefinition = InterfaceTypeDefinition
-    <$  tok "interface"
-    <*> name
-    <*> fieldDefinitions
-
-unionTypeDefinition :: Parser UnionTypeDefinition
-unionTypeDefinition = UnionTypeDefinition
-    <$  tok "union"
-    <*> name
-    <*  tok "="
-    <*> unionMembers
-
-unionMembers :: Parser [NamedType]
-unionMembers = namedType `sepBy1` tok "|"
-
-scalarTypeDefinition :: Parser ScalarTypeDefinition
-scalarTypeDefinition = ScalarTypeDefinition
-    <$  tok "scalar"
-    <*> name
-
-enumTypeDefinition :: Parser EnumTypeDefinition
-enumTypeDefinition = EnumTypeDefinition
-    <$  tok "enum"
-    <*> name
-    <*> enumValueDefinitions
-
-enumValueDefinitions :: Parser [EnumValueDefinition]
-enumValueDefinitions = braces $ many1 enumValueDefinition
-
-enumValueDefinition :: Parser EnumValueDefinition
-enumValueDefinition = EnumValueDefinition <$> name
-
-inputObjectTypeDefinition :: Parser InputObjectTypeDefinition
-inputObjectTypeDefinition = InputObjectTypeDefinition
-    <$  tok "input"
-    <*> name
-    <*> inputValueDefinitions
-
-typeExtensionDefinition :: Parser TypeExtensionDefinition
-typeExtensionDefinition = TypeExtensionDefinition
-    <$  tok "extend"
-    <*> objectTypeDefinition
-
--- * Internal
-
-tok :: Parser a -> Parser a
-tok p = p <* whiteSpace
-
-parens :: Parser a -> Parser a
-parens = between "(" ")"
-
-braces :: Parser a -> Parser a
-braces = between "{" "}"
-
-quotes :: Parser a -> Parser a
-quotes = between "\"" "\""
-
-brackets :: Parser a -> Parser a
-brackets = between "[" "]"
-
-between :: Parser Text -> Parser Text -> Parser a -> Parser a
-between open close p = tok open *> p <* tok close
-
--- `empty` /= `pure mempty` for `Parser`.
-optempty :: Monoid a => Parser a -> Parser a
-optempty = option mempty
-
--- ** WhiteSpace
---
-whiteSpace :: Parser ()
-whiteSpace = peekChar >>= \case
-    Just c -> if isSpace c || c == ','
-              then anyChar *> whiteSpace
-              else when (c == '#') $ manyTill anyChar endOfLine *> whiteSpace
-    _ -> return ()

LICENSE

@@ -1,4 +1,5 @@
-Copyright J. Daniel Navarro (c) 2015
+Copyright 2019-2020 Eugen Wissner, Germany
+Copyright 2015-2017 J. Daniel Navarro
 
 All rights reserved.
 

LICENSE.MPL

@@ -0,0 +1,373 @@
+Mozilla Public License Version 2.0
+==================================
+
+1. Definitions
+--------------
+
+1.1. "Contributor"
+    means each individual or legal entity that creates, contributes to
+    the creation of, or owns Covered Software.
+
+1.2. "Contributor Version"
+    means the combination of the Contributions of others (if any) used
+    by a Contributor and that particular Contributor's Contribution.
+
+1.3. "Contribution"
+    means Covered Software of a particular Contributor.
+
+1.4. "Covered Software"
+    means Source Code Form to which the initial Contributor has attached
+    the notice in Exhibit A, the Executable Form of such Source Code
+    Form, and Modifications of such Source Code Form, in each case
+    including portions thereof.
+
+1.5. "Incompatible With Secondary Licenses"
+    means
+
+    (a) that the initial Contributor has attached the notice described
+        in Exhibit B to the Covered Software; or
+
+    (b) that the Covered Software was made available under the terms of
+        version 1.1 or earlier of the License, but not also under the
+        terms of a Secondary License.
+
+1.6. "Executable Form"
+    means any form of the work other than Source Code Form.
+
+1.7. "Larger Work"
+    means a work that combines Covered Software with other material, in
+    a separate file or files, that is not Covered Software.
+
+1.8. "License"
+    means this document.
+
+1.9. "Licensable"
+    means having the right to grant, to the maximum extent possible,
+    whether at the time of the initial grant or subsequently, any and
+    all of the rights conveyed by this License.
+
+1.10. "Modifications"
+    means any of the following:
+
+    (a) any file in Source Code Form that results from an addition to,
+        deletion from, or modification of the contents of Covered
+        Software; or
+
+    (b) any new file in Source Code Form that contains any Covered
+        Software.
+
+1.11. "Patent Claims" of a Contributor
+    means any patent claim(s), including without limitation, method,
+    process, and apparatus claims, in any patent Licensable by such
+    Contributor that would be infringed, but for the grant of the
+    License, by the making, using, selling, offering for sale, having
+    made, import, or transfer of either its Contributions or its
+    Contributor Version.
+
+1.12. "Secondary License"
+    means either the GNU General Public License, Version 2.0, the GNU
+    Lesser General Public License, Version 2.1, the GNU Affero General
+    Public License, Version 3.0, or any later versions of those
+    licenses.
+
+1.13. "Source Code Form"
+    means the form of the work preferred for making modifications.
+
+1.14. "You" (or "Your")
+    means an individual or a legal entity exercising rights under this
+    License. For legal entities, "You" includes any entity that
+    controls, is controlled by, or is under common control with You. For
+    purposes of this definition, "control" means (a) the power, direct
+    or indirect, to cause the direction or management of such entity,
+    whether by contract or otherwise, or (b) ownership of more than
+    fifty percent (50%) of the outstanding shares or beneficial
+    ownership of such entity.
+
+2. License Grants and Conditions
+--------------------------------
+
+2.1. Grants
+
+Each Contributor hereby grants You a world-wide, royalty-free,
+non-exclusive license:
+
+(a) under intellectual property rights (other than patent or trademark)
+    Licensable by such Contributor to use, reproduce, make available,
+    modify, display, perform, distribute, and otherwise exploit its
+    Contributions, either on an unmodified basis, with Modifications, or
+    as part of a Larger Work; and
+
+(b) under Patent Claims of such Contributor to make, use, sell, offer
+    for sale, have made, import, and otherwise transfer either its
+    Contributions or its Contributor Version.
+
+2.2. Effective Date
+
+The licenses granted in Section 2.1 with respect to any Contribution
+become effective for each Contribution on the date the Contributor first
+distributes such Contribution.
+
+2.3. Limitations on Grant Scope
+
+The licenses granted in this Section 2 are the only rights granted under
+this License. No additional rights or licenses will be implied from the
+distribution or licensing of Covered Software under this License.
+Notwithstanding Section 2.1(b) above, no patent license is granted by a
+Contributor:
+
+(a) for any code that a Contributor has removed from Covered Software;
+    or
+
+(b) for infringements caused by: (i) Your and any other third party's
+    modifications of Covered Software, or (ii) the combination of its
+    Contributions with other software (except as part of its Contributor
+    Version); or
+
+(c) under Patent Claims infringed by Covered Software in the absence of
+    its Contributions.
+
+This License does not grant any rights in the trademarks, service marks,
+or logos of any Contributor (except as may be necessary to comply with
+the notice requirements in Section 3.4).
+
+2.4. Subsequent Licenses
+
+No Contributor makes additional grants as a result of Your choice to
+distribute the Covered Software under a subsequent version of this
+License (see Section 10.2) or under the terms of a Secondary License (if
+permitted under the terms of Section 3.3).
+
+2.5. Representation
+
+Each Contributor represents that the Contributor believes its
+Contributions are its original creation(s) or it has sufficient rights
+to grant the rights to its Contributions conveyed by this License.
+
+2.6. Fair Use
+
+This License is not intended to limit any rights You have under
+applicable copyright doctrines of fair use, fair dealing, or other
+equivalents.
+
+2.7. Conditions
+
+Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted
+in Section 2.1.
+
+3. Responsibilities
+-------------------
+
+3.1. Distribution of Source Form
+
+All distribution of Covered Software in Source Code Form, including any
+Modifications that You create or to which You contribute, must be under
+the terms of this License. You must inform recipients that the Source
+Code Form of the Covered Software is governed by the terms of this
+License, and how they can obtain a copy of this License. You may not
+attempt to alter or restrict the recipients' rights in the Source Code
+Form.
+
+3.2. Distribution of Executable Form
+
+If You distribute Covered Software in Executable Form then:
+
+(a) such Covered Software must also be made available in Source Code
+    Form, as described in Section 3.1, and You must inform recipients of
+    the Executable Form how they can obtain a copy of such Source Code
+    Form by reasonable means in a timely manner, at a charge no more
+    than the cost of distribution to the recipient; and
+
+(b) You may distribute such Executable Form under the terms of this
+    License, or sublicense it under different terms, provided that the
+    license for the Executable Form does not attempt to limit or alter
+    the recipients' rights in the Source Code Form under this License.
+
+3.3. Distribution of a Larger Work
+
+You may create and distribute a Larger Work under terms of Your choice,
+provided that You also comply with the requirements of this License for
+the Covered Software. If the Larger Work is a combination of Covered
+Software with a work governed by one or more Secondary Licenses, and the
+Covered Software is not Incompatible With Secondary Licenses, this
+License permits You to additionally distribute such Covered Software
+under the terms of such Secondary License(s), so that the recipient of
+the Larger Work may, at their option, further distribute the Covered
+Software under the terms of either this License or such Secondary
+License(s).
+
+3.4. Notices
+
+You may not remove or alter the substance of any license notices
+(including copyright notices, patent notices, disclaimers of warranty,
+or limitations of liability) contained within the Source Code Form of
+the Covered Software, except that You may alter any license notices to
+the extent required to remedy known factual inaccuracies.
+
+3.5. Application of Additional Terms
+
+You may choose to offer, and to charge a fee for, warranty, support,
+indemnity or liability obligations to one or more recipients of Covered
+Software. However, You may do so only on Your own behalf, and not on
+behalf of any Contributor. You must make it absolutely clear that any
+such warranty, support, indemnity, or liability obligation is offered by
+You alone, and You hereby agree to indemnify every Contributor for any
+liability incurred by such Contributor as a result of warranty, support,
+indemnity or liability terms You offer. You may include additional
+disclaimers of warranty and limitations of liability specific to any
+jurisdiction.
+
+4. Inability to Comply Due to Statute or Regulation
+---------------------------------------------------
+
+If it is impossible for You to comply with any of the terms of this
+License with respect to some or all of the Covered Software due to
+statute, judicial order, or regulation then You must: (a) comply with
+the terms of this License to the maximum extent possible; and (b)
+describe the limitations and the code they affect. Such description must
+be placed in a text file included with all distributions of the Covered
+Software under this License. Except to the extent prohibited by statute
+or regulation, such description must be sufficiently detailed for a
+recipient of ordinary skill to be able to understand it.
+
+5. Termination
+--------------
+
+5.1. The rights granted under this License will terminate automatically
+if You fail to comply with any of its terms. However, if You become
+compliant, then the rights granted under this License from a particular
+Contributor are reinstated (a) provisionally, unless and until such
+Contributor explicitly and finally terminates Your grants, and (b) on an
+ongoing basis, if such Contributor fails to notify You of the
+non-compliance by some reasonable means prior to 60 days after You have
+come back into compliance. Moreover, Your grants from a particular
+Contributor are reinstated on an ongoing basis if such Contributor
+notifies You of the non-compliance by some reasonable means, this is the
+first time You have received notice of non-compliance with this License
+from such Contributor, and You become compliant prior to 30 days after
+Your receipt of the notice.
+
+5.2. If You initiate litigation against any entity by asserting a patent
+infringement claim (excluding declaratory judgment actions,
+counter-claims, and cross-claims) alleging that a Contributor Version
+directly or indirectly infringes any patent, then the rights granted to
+You by any and all Contributors for the Covered Software under Section
+2.1 of this License shall terminate.
+
+5.3. In the event of termination under Sections 5.1 or 5.2 above, all
+end user license agreements (excluding distributors and resellers) which
+have been validly granted by You or Your distributors under this License
+prior to termination shall survive termination.
+
+************************************************************************
+*                                                                      *
+*  6. Disclaimer of Warranty                                           *
+*  -------------------------                                           *
+*                                                                      *
+*  Covered Software is provided under this License on an "as is"       *
+*  basis, without warranty of any kind, either expressed, implied, or  *
+*  statutory, including, without limitation, warranties that the       *
+*  Covered Software is free of defects, merchantable, fit for a        *
+*  particular purpose or non-infringing. The entire risk as to the     *
+*  quality and performance of the Covered Software is with You.        *
+*  Should any Covered Software prove defective in any respect, You     *
+*  (not any Contributor) assume the cost of any necessary servicing,   *
+*  repair, or correction. This disclaimer of warranty constitutes an   *
+*  essential part of this License. No use of any Covered Software is   *
+*  authorized under this License except under this disclaimer.         *
+*                                                                      *
+************************************************************************
+
+************************************************************************
+*                                                                      *
+*  7. Limitation of Liability                                          *
+*  --------------------------                                          *
+*                                                                      *
+*  Under no circumstances and under no legal theory, whether tort      *
+*  (including negligence), contract, or otherwise, shall any           *
+*  Contributor, or anyone who distributes Covered Software as          *
+*  permitted above, be liable to You for any direct, indirect,         *
+*  special, incidental, or consequential damages of any character      *
+*  including, without limitation, damages for lost profits, loss of    *
+*  goodwill, work stoppage, computer failure or malfunction, or any    *
+*  and all other commercial damages or losses, even if such party      *
+*  shall have been informed of the possibility of such damages. This   *
+*  limitation of liability shall not apply to liability for death or   *
+*  personal injury resulting from such party's negligence to the       *
+*  extent applicable law prohibits such limitation. Some               *
+*  jurisdictions do not allow the exclusion or limitation of           *
+*  incidental or consequential damages, so this exclusion and          *
+*  limitation may not apply to You.                                    *
+*                                                                      *
+************************************************************************
+
+8. Litigation
+-------------
+
+Any litigation relating to this License may be brought only in the
+courts of a jurisdiction where the defendant maintains its principal
+place of business and such litigation shall be governed by laws of that
+jurisdiction, without reference to its conflict-of-law provisions.
+Nothing in this Section shall prevent a party's ability to bring
+cross-claims or counter-claims.
+
+9. Miscellaneous
+----------------
+
+This License represents the complete agreement concerning the subject
+matter hereof. If any provision of this License is held to be
+unenforceable, such provision shall be reformed only to the extent
+necessary to make it enforceable. Any law or regulation which provides
+that the language of a contract shall be construed against the drafter
+shall not be used to construe this License against a Contributor.
+
+10. Versions of the License
+---------------------------
+
+10.1. New Versions
+
+Mozilla Foundation is the license steward. Except as provided in Section
+10.3, no one other than the license steward has the right to modify or
+publish new versions of this License. Each version will be given a
+distinguishing version number.
+
+10.2. Effect of New Versions
+
+You may distribute the Covered Software under the terms of the version
+of the License under which You originally received the Covered Software,
+or under the terms of any subsequent version published by the license
+steward.
+
+10.3. Modified Versions
+
+If you create software not governed by this License, and you want to
+create a new license for such software, you may create and use a
+modified version of this License if you rename the license and remove
+any references to the name of the license steward (except to note that
+such modified license differs from this License).
+
+10.4. Distributing Source Code Form that is Incompatible With Secondary
+Licenses
+
+If You choose to distribute Source Code Form that is Incompatible With
+Secondary Licenses under the terms of this version of the License, the
+notice described in Exhibit B of this License must be attached.
+
+Exhibit A - Source Code Form License Notice
+-------------------------------------------
+
+  This Source Code Form is subject to the terms of the Mozilla Public
+  License, v. 2.0. If a copy of the MPL was not distributed with this
+  file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+If it is not possible or desirable to put the notice in a particular
+file, then You may include the notice in a location (such as a LICENSE
+file in a relevant directory) where a recipient would be likely to look
+for such a notice.
+
+You may add additional accurate notices of copyright ownership.
+
+Exhibit B - "Incompatible With Secondary Licenses" Notice
+---------------------------------------------------------
+
+  This Source Code Form is "Incompatible With Secondary Licenses", as
+  defined by the Mozilla Public License, v. 2.0.

README.md

@@ -1,25 +1,12 @@
-# Haskell GraphQL
+# GraphQL implementation in Haskell
 
-[![Hackage Version](https://img.shields.io/hackage/v/graphql.svg)](https://hackage.haskell.org/package/graphql)
+See https://git.caraus.tech/OSS/graphql.
 
-For now this only provides the data types to represent the GraphQL AST,
-but the idea is to be a Haskell port of
-[`graphql-js`](https://github.com/graphql/graphql-js). Next releases
-should include:
+Report issues on the
+[bug tracker](https://git.caraus.tech/OSS/graphql/issues).
 
-- [x] GraphQL AST
-- [x] Parser for the GraphQL language. See TODO for caveats.
-- [ ] GraphQL Schema AST.
-- [ ] Parser for the GraphQL Schema language.
-- [ ] Interpreter of GraphQL requests.
-- [ ] Utilities to define GraphQL types and schema.
+API documentation is available through
+[Hackage](https://hackage.haskell.org/package/graphql).
 
-See the TODO file for more concrete tasks.
-
-## Contact
-
-Suggestions, contributions and bug reports are welcome.
-
-Feel free to contact me, jdnavarro, on the #haskell channel on the
-[GraphQL Slack Server](https://graphql.slack.com). You can obtain an
-invitation [here](https://graphql-slack.herokuapp.com/).
+Further documentation will be made available in the
+[Wiki](https://git.caraus.tech/OSS/graphql/wiki).

TODO

@@ -1,21 +0,0 @@
-## AST
-- Simplify unnecessary `newtypes` with type synonyms
-- Data type accessors
-- Deal with Strictness/unboxing
-- Deal with Location
-
-## Parser
-- Secure Names
-- Optimize `name` and `whiteSpace`: `take...`, `T.fold`, ...
-- Handle escape characters in string literals
-- Guard for `on` in `FragmentSpread`
-- Tests!
-- Handle `[Const]` grammar parameter. Need examples
-- Arbitrary precision for number values?
-- Handle errors. Perhaps port to `parsers` or use a lexer and
- `regex-applicative`
-
-## Tests
-
-- Golden data within package, `path_graphql` macro.
-- Pretty Print golden result

graphql.cabal

@@ -1,45 +1,108 @@
+cabal-version: 3.0
+
 name:           graphql
-version:             0.2
+version:        1.4.0.0
 synopsis:       Haskell GraphQL implementation
-description:
-  This package provides a rudimentary parser for the
-  <https://facebook.github.io/graphql/ GraphQL> language.
-homepage:            https://github.com/jdnavarro/graphql-haskell
-bug-reports:         https://github.com/jdnavarro/graphql-haskell/issues
-license:             BSD3
-license-file:        LICENSE
-author:              Danny Navarro
-maintainer:          j@dannynavarro.net
-copyright:           Copyright (C) 2015 J. Daniel Navarro
-category:            Web
+description:    Haskell <https://spec.graphql.org/June2018/ GraphQL> implementation.
+category:       Language
+homepage:       https://git.caraus.tech/OSS/graphql
+bug-reports:    https://git.caraus.tech/OSS/graphql/issues
+author:         Danny Navarro <j@dannynavarro.net>,
+                Matthías Páll Gissurarson <mpg@mpg.is>,
+                Sólrún Halla Einarsdóttir <she@mpg.is>
+maintainer:     belka@caraus.de
+copyright:      (c) 2019-2024 Eugen Wissner,
+                (c) 2015-2017 J. Daniel Navarro
+license:        MPL-2.0 AND BSD-3-Clause
+license-files:  LICENSE,
+                LICENSE.MPL
 build-type:     Simple
-cabal-version:       >=1.10
-tested-with:         GHC == 7.10
-extra-source-files:  README.md CHANGELOG.md stack.yaml
-
-library
-  default-language:    Haskell2010
-  ghc-options:         -Wall
-  exposed-modules:     Data.GraphQL.AST
-                       Data.GraphQL.Parser
-  build-depends:       base >= 4.7 && < 5,
-                       text >=0.11.3.1,
-                       attoparsec >=0.10.4.0
-
-test-suite golden
-  default-language:    Haskell2010
-  type:                exitcode-stdio-1.0
-  hs-source-dirs:      tests
-  main-is:             golden.hs
-  ghc-options:         -Wall
-  build-depends:       base >= 4.6 && <5,
-                       bytestring,
-                       text,
-                       attoparsec,
-                       tasty >=0.10,
-                       tasty-golden,
-                       graphql
+extra-source-files:
+  CHANGELOG.md
+  README.md
+tested-with:
+  GHC == 9.8.2
 
 source-repository head
   type: git
-  location: git://github.com/jdnavarro/graphql-haskell.git
+  location: https://git.caraus.tech/OSS/graphql.git
+
+library
+  exposed-modules:
+    Language.GraphQL
+    Language.GraphQL.AST
+    Language.GraphQL.AST.DirectiveLocation
+    Language.GraphQL.AST.Document
+    Language.GraphQL.AST.Encoder
+    Language.GraphQL.AST.Lexer
+    Language.GraphQL.AST.Parser
+    Language.GraphQL.Error
+    Language.GraphQL.Execute
+    Language.GraphQL.Execute.Coerce
+    Language.GraphQL.Execute.OrderedMap
+    Language.GraphQL.Type
+    Language.GraphQL.Type.In
+    Language.GraphQL.Type.Out
+    Language.GraphQL.Type.Schema
+    Language.GraphQL.Validate
+    Language.GraphQL.Validate.Validation
+  other-modules:
+    Language.GraphQL.Execute.Transform
+    Language.GraphQL.Type.Definition
+    Language.GraphQL.Type.Internal
+    Language.GraphQL.Validate.Rules
+  hs-source-dirs:
+    src
+  ghc-options: -Wall
+
+  build-depends:
+    base >= 4.15 && < 5,
+    conduit ^>= 1.3.4,
+    containers >= 0.6 && < 0.8,
+    exceptions ^>= 0.10.4,
+    megaparsec >= 9.0 && < 10,
+    parser-combinators >= 1.3 && < 2,
+    text >= 1.2 && < 3,
+    transformers >= 0.5.6 && < 0.7,
+    unordered-containers ^>= 0.2.14,
+    vector >= 0.12 && < 0.14
+
+  default-language: Haskell2010
+
+test-suite graphql-test
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  other-modules:
+    Language.GraphQL.AST.DocumentSpec
+    Language.GraphQL.AST.EncoderSpec
+    Language.GraphQL.AST.LexerSpec
+    Language.GraphQL.AST.ParserSpec
+    Language.GraphQL.AST.Arbitrary
+    Language.GraphQL.ErrorSpec
+    Language.GraphQL.Execute.CoerceSpec
+    Language.GraphQL.Execute.OrderedMapSpec
+    Language.GraphQL.ExecuteSpec
+    Language.GraphQL.Type.OutSpec
+    Language.GraphQL.Validate.RulesSpec
+    Schemas.HeroSchema
+  hs-source-dirs:
+    tests
+  ghc-options: -threaded -rtsopts -with-rtsopts=-N -Wall
+
+  build-depends:
+    QuickCheck >= 2.14 && < 2.16,
+    base,
+    conduit,
+    exceptions,
+    graphql,
+    hspec >= 2.10.9 && < 2.12,
+    hspec-expectations ^>= 0.8.2,
+    hspec-megaparsec ^>= 2.2.0,
+    megaparsec,
+    text,
+    unordered-containers,
+    containers,
+    vector
+  build-tool-depends:
+    hspec-discover:hspec-discover
+  default-language: Haskell2010

src/Language/GraphQL.hs

@@ -0,0 +1,46 @@
+{-# LANGUAGE RecordWildCards #-}
+
+-- | This module provides the functions to parse and execute @GraphQL@ queries.
+module Language.GraphQL
+    ( graphql
+    ) where
+
+import Control.Monad.Catch (MonadCatch)
+import Data.HashMap.Strict (HashMap)
+import qualified Data.Sequence as Seq
+import Data.Text (Text)
+import qualified Data.Text as Text
+import qualified Language.GraphQL.AST as Full
+import Language.GraphQL.Error
+import Language.GraphQL.Execute
+import qualified Language.GraphQL.Validate as Validate
+import Language.GraphQL.Type.Schema (Schema)
+import Prelude hiding (null)
+import Text.Megaparsec (parse)
+
+-- | If the text parses correctly as a @GraphQL@ query the query is
+-- executed using the given 'Schema'.
+--
+-- An operation name can be given if the document contains multiple operations.
+graphql :: (MonadCatch m, VariableValue a, Serialize b)
+    => Schema m -- ^ Resolvers.
+    -> Maybe Text -- ^ Operation name.
+    -> HashMap Full.Name a -- ^ Variable substitution function.
+    -> Text -- ^ Text representing a @GraphQL@ request document.
+    -> m (Either (ResponseEventStream m b) (Response b)) -- ^ Response.
+graphql schema operationName variableValues document' =
+    case parse Full.document "" document' of
+        Left errorBundle -> pure  <$> parseError errorBundle
+        Right parsed ->
+            case validate parsed of
+                Seq.Empty -> execute schema operationName variableValues parsed
+                errors -> pure $ pure
+                    $ Response null
+                    $ fromValidationError <$> errors
+  where
+    validate = Validate.document schema Validate.specifiedRules
+    fromValidationError Validate.Error{..} = Error
+        { message = Text.pack message
+        , locations = locations
+        , path = []
+        }

src/Language/GraphQL/AST.hs

@@ -0,0 +1,10 @@
+{-# LANGUAGE Safe #-}
+
+-- | Target AST for parser.
+module Language.GraphQL.AST
+    ( module Language.GraphQL.AST.Document
+    , module Language.GraphQL.AST.Parser
+    ) where
+
+import Language.GraphQL.AST.Document
+import Language.GraphQL.AST.Parser

src/Language/GraphQL/AST/DirectiveLocation.hs

@@ -0,0 +1,71 @@
+{-# LANGUAGE Safe #-}
+
+-- | Various parts of a GraphQL document can be annotated with directives.
+-- This module describes locations in a document where directives can appear.
+module Language.GraphQL.AST.DirectiveLocation
+    ( DirectiveLocation(..)
+    , ExecutableDirectiveLocation(..)
+    , TypeSystemDirectiveLocation(..)
+    ) where
+
+-- | All directives can be splitted in two groups: directives used to annotate
+-- various parts of executable definitions and the ones used in the schema
+-- definition.
+data DirectiveLocation
+    = ExecutableDirectiveLocation ExecutableDirectiveLocation
+    | TypeSystemDirectiveLocation TypeSystemDirectiveLocation
+    deriving Eq
+
+instance Show DirectiveLocation where
+    show (ExecutableDirectiveLocation directiveLocation) =
+        show directiveLocation
+    show (TypeSystemDirectiveLocation directiveLocation) =
+        show directiveLocation
+
+-- | Where directives can appear in an executable definition, like a query.
+data ExecutableDirectiveLocation
+    = Query
+    | Mutation
+    | Subscription
+    | Field
+    | FragmentDefinition
+    | FragmentSpread
+    | InlineFragment
+    deriving Eq
+
+instance Show ExecutableDirectiveLocation where
+    show Query = "QUERY"
+    show Mutation = "MUTATION"
+    show Subscription = "SUBSCRIPTION"
+    show Field = "FIELD"
+    show FragmentDefinition = "FRAGMENT_DEFINITION"
+    show FragmentSpread = "FRAGMENT_SPREAD"
+    show InlineFragment = "INLINE_FRAGMENT"
+
+-- | Where directives can appear in a type system definition.
+data TypeSystemDirectiveLocation
+    = Schema
+    | Scalar
+    | Object
+    | FieldDefinition
+    | ArgumentDefinition
+    | Interface
+    | Union
+    | Enum
+    | EnumValue
+    | InputObject
+    | InputFieldDefinition
+    deriving Eq
+
+instance Show TypeSystemDirectiveLocation where
+    show Schema = "SCHEMA"
+    show Scalar = "SCALAR"
+    show Object = "OBJECT"
+    show FieldDefinition = "FIELD_DEFINITION"
+    show ArgumentDefinition = "ARGUMENT_DEFINITION"
+    show Interface = "INTERFACE"
+    show Union = "UNION"
+    show Enum = "ENUM"
+    show EnumValue = "ENUM_VALUE"
+    show InputObject = "INPUT_OBJECT"
+    show InputFieldDefinition = "INPUT_FIELD_DEFINITION"

src/Language/GraphQL/AST/Document.hs

@@ -0,0 +1,630 @@
+{-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE Safe #-}
+
+-- | This module defines an abstract syntax tree for the @GraphQL@ language. It
+-- follows closely the structure given in the specification. Please refer to
+-- <https://facebook.github.io/graphql/ Facebook's GraphQL Specification>.
+-- for more information.
+module Language.GraphQL.AST.Document
+    ( Argument(..)
+    , ArgumentsDefinition(..)
+    , ConstValue(..)
+    , Definition(..)
+    , Description(..)
+    , Directive(..)
+    , Document
+    , EnumValueDefinition(..)
+    , ExecutableDefinition(..)
+    , Field(..)
+    , FieldDefinition(..)
+    , FragmentDefinition(..)
+    , FragmentSpread(..)
+    , ImplementsInterfaces(..)
+    , InlineFragment(..)
+    , InputValueDefinition(..)
+    , Location(..)
+    , Name
+    , NamedType
+    , Node(..)
+    , NonNullType(..)
+    , ObjectField(..)
+    , OperationDefinition(..)
+    , OperationType(..)
+    , OperationTypeDefinition(..)
+    , SchemaExtension(..)
+    , Selection(..)
+    , SelectionSet
+    , SelectionSetOpt
+    , Type(..)
+    , TypeCondition
+    , TypeDefinition(..)
+    , TypeExtension(..)
+    , TypeSystemDefinition(..)
+    , TypeSystemExtension(..)
+    , UnionMemberTypes(..)
+    , Value(..)
+    , VariableDefinition(..)
+    , escape
+    , showVariableName
+    , showVariable
+    ) where
+
+import Data.Char (ord)
+import Data.Foldable (toList)
+import Data.Int (Int32)
+import Data.List (intercalate)
+import Data.List.NonEmpty (NonEmpty)
+import Numeric (showFloat, showHex)
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Language.GraphQL.AST.DirectiveLocation (DirectiveLocation)
+
+-- * Language
+
+-- ** Source Text
+
+-- | Name.
+type Name = Text
+
+-- | Error location, line and column.
+data Location = Location
+    { line :: Word
+    , column :: Word
+    } deriving (Eq, Show)
+
+instance Ord Location where
+    compare (Location thisLine thisColumn) (Location thatLine thatColumn)
+        | thisLine < thatLine = LT
+        | thisLine > thatLine = GT
+        | otherwise = compare thisColumn thatColumn
+
+-- | Contains some tree node with a location.
+data Node a = Node
+    { node :: a
+    , location :: Location
+    } deriving Eq
+
+instance Show a => Show (Node a) where
+    show Node{ node } = show node
+
+instance Functor Node where
+    fmap f Node{..} = Node (f node) location
+
+-- ** Document
+
+-- | GraphQL document.
+type Document = NonEmpty Definition
+
+-- | All kinds of definitions that can occur in a GraphQL document.
+data Definition
+    = ExecutableDefinition ExecutableDefinition
+    | TypeSystemDefinition TypeSystemDefinition Location
+    | TypeSystemExtension TypeSystemExtension Location
+    deriving (Eq, Show)
+
+-- | Top-level definition of a document, either an operation or a fragment.
+data ExecutableDefinition
+    = DefinitionOperation OperationDefinition
+    | DefinitionFragment FragmentDefinition
+    deriving (Eq, Show)
+
+-- ** Operations
+
+-- | Operation definition.
+data OperationDefinition
+    = SelectionSet SelectionSet Location
+    | OperationDefinition
+        OperationType
+        (Maybe Name)
+        [VariableDefinition]
+        [Directive]
+        SelectionSet
+        Location
+    deriving (Eq, Show)
+
+-- | GraphQL has 3 operation types:
+--
+-- * query - a read-only fetch.
+-- * mutation - a write operation followed by a fetch.
+-- * subscription - a long-lived request that fetches data in response to
+-- source events.
+data OperationType = Query | Mutation | Subscription deriving (Eq, Show)
+
+-- ** Selection Sets
+
+-- | "Top-level" selection, selection on an operation or fragment.
+type SelectionSet = NonEmpty Selection
+
+-- | Field selection.
+type SelectionSetOpt = [Selection]
+
+-- | Selection is a single entry in a selection set. It can be a single 'Field',
+-- 'FragmentSpread' or an 'InlineFragment'.
+data Selection
+    = FieldSelection Field
+    | FragmentSpreadSelection FragmentSpread
+    | InlineFragmentSelection InlineFragment
+    deriving (Eq, Show)
+
+-- | The only required property of a field is its name. Optionally it can also
+-- have an alias, arguments, directives and a list of subfields.
+--
+-- In the following query "user" is a field with two subfields, "id" and "name":
+--
+-- @
+-- {
+--   user {
+--     id
+--     name
+--   }
+-- }
+-- @
+data Field =
+    Field (Maybe Name) Name [Argument] [Directive] SelectionSetOpt Location
+    deriving (Eq, Show)
+
+-- | Inline fragments don't have any name and the type condition ("on UserType")
+-- is optional.
+--
+-- @
+-- {
+--   user {
+--     ... on UserType {
+--       id
+--       name
+--     }
+-- }
+-- @
+data InlineFragment = InlineFragment
+    (Maybe TypeCondition) [Directive] SelectionSet Location
+    deriving (Eq, Show)
+
+-- | A fragment spread refers to a fragment defined outside the operation and is
+-- expanded at the execution time.
+--
+-- @
+-- {
+--   user {
+--     ...userFragment
+--   }
+-- }
+--
+-- fragment userFragment on UserType {
+--   id
+--   name
+-- }
+-- @
+data FragmentSpread = FragmentSpread Name [Directive] Location
+    deriving (Eq, Show)
+
+-- ** Arguments
+
+-- | Single argument.
+--
+-- @
+-- {
+--   user(id: 4) {
+--     name
+--   }
+-- }
+-- @
+--
+--  Here "id" is an argument for the field "user" and its value is 4.
+data Argument = Argument Name (Node Value) Location deriving (Eq, Show)
+
+-- ** Fragments
+
+-- | Fragment definition.
+data FragmentDefinition
+    = FragmentDefinition Name TypeCondition [Directive] SelectionSet Location
+    deriving (Eq, Show)
+
+-- | Type condition.
+type TypeCondition = Name
+
+-- ** Input Values
+
+-- | Escapes a single character according to the GraphQL escaping rules for
+-- double-quoted string values.
+--
+-- Characters, that should be escaped, are written as escaped characters with a
+-- backslash or Unicode with an \"\\u\". Other characters are returned as
+-- strings.
+escape :: Char -> String
+escape char'
+    | char' == '\\' = "\\\\"
+    | char' == '\"' = "\\\""
+    | char' == '\b' = "\\b"
+    | char' == '\f' = "\\f"
+    | char' == '\n' = "\\n"
+    | char' == '\r' = "\\r"
+    | char' == '\t' = "\\t"
+    | char' < '\x0010' = unicode  "\\u000" char'
+    | char' < '\x0020' = unicode "\\u00" char'
+    | otherwise = [char']
+  where
+    unicode prefix uchar = prefix <> (showHex $ ord uchar) ""
+
+showList' :: Show a => [a] -> String
+showList' list = "[" ++ intercalate ", " (show <$> list) ++ "]"
+
+showObject :: Show a => [ObjectField a] -> String
+showObject fields =
+    "{ " ++ intercalate ", " (show <$> fields) ++ " }"
+
+-- | Input value (literal or variable).
+data Value
+    = Variable Name
+    | Int Int32
+    | Float Double
+    | String Text
+    | Boolean Bool
+    | Null
+    | Enum Name
+    | List [Node Value]
+    | Object [ObjectField Value]
+    deriving Eq
+
+instance Show Value where
+    showList = mappend . showList'
+    show (Variable variableName) = '$' : Text.unpack variableName
+    show (Int integer) = show integer
+    show (Float float) = show $ ConstFloat float
+    show (String text) = show $  ConstString text
+    show (Boolean boolean) = show boolean
+    show Null = "null"
+    show (Enum name) = Text.unpack name
+    show (List list) = show list
+    show (Object fields) = showObject fields
+
+-- | Constant input value.
+data ConstValue
+    = ConstInt Int32
+    | ConstFloat Double
+    | ConstString Text
+    | ConstBoolean Bool
+    | ConstNull
+    | ConstEnum Name
+    | ConstList [Node ConstValue]
+    | ConstObject [ObjectField ConstValue]
+    deriving Eq
+
+instance Show ConstValue where
+    showList = mappend . showList'
+    show (ConstInt integer) = show integer
+    show (ConstFloat float) = showFloat float mempty
+    show (ConstString text) = "\"" <> Text.foldr (mappend . escape) "\"" text
+    show (ConstBoolean boolean) = show boolean
+    show ConstNull = "null"
+    show (ConstEnum name) = Text.unpack name
+    show (ConstList list) = show list
+    show (ConstObject fields) = showObject fields
+
+-- | Key-value pair.
+--
+-- A list of 'ObjectField's represents a GraphQL object type.
+data ObjectField a = ObjectField
+    { name :: Name
+    , value :: Node a
+    , location :: Location
+    } deriving Eq
+
+instance Show a => Show (ObjectField a) where
+    show ObjectField{..} = Text.unpack name ++ ": " ++ show value
+
+instance Functor ObjectField where
+    fmap f ObjectField{..} = ObjectField name (f <$> value) location
+
+-- ** Variables
+
+-- | Variable definition.
+--
+-- Each operation can include a list of variables:
+--
+-- @
+-- query (protagonist: String = \"Zarathustra\") {
+--   getAuthor(protagonist: $protagonist)
+-- }
+-- @
+--
+-- This query defines an optional variable @protagonist@ of type @String@,
+-- its default value is \"Zarathustra\". If no default value is defined and no
+-- value is provided, a variable can still be @null@ if its type is nullable.
+--
+-- Variables are usually passed along with the query, but not in the query
+-- itself. They make queries reusable.
+data VariableDefinition =
+    VariableDefinition Name Type (Maybe (Node ConstValue)) Location
+    deriving (Eq, Show)
+
+showVariableName :: VariableDefinition -> String
+showVariableName (VariableDefinition name _ _ _) = "$" <> Text.unpack name
+
+showVariable :: VariableDefinition -> String
+showVariable var@(VariableDefinition _ type' _ _) = showVariableName var <> ":" <> " " <> show type'
+
+-- ** Type References
+
+-- | Type representation.
+data Type
+    = TypeNamed Name
+    | TypeList Type
+    | TypeNonNull NonNullType
+    deriving Eq
+
+instance Show Type where
+    show (TypeNamed typeName) = Text.unpack typeName
+    show (TypeList listType) = concat ["[", show listType, "]"]
+    show (TypeNonNull nonNullType) = show nonNullType
+
+-- | Represents type names.
+type NamedType = Name
+
+-- | Helper type to represent Non-Null types and lists of such types.
+data NonNullType
+    = NonNullTypeNamed Name
+    | NonNullTypeList Type
+    deriving Eq
+
+instance Show NonNullType where
+    show (NonNullTypeNamed typeName) = Text.unpack $ typeName <> "!"
+    show (NonNullTypeList listType) = concat ["[", show listType, "]!"]
+
+-- ** Directives
+
+-- | Directive.
+--
+-- Directives begin with "@", can accept arguments, and can be applied to the
+-- most GraphQL elements, providing additional information.
+data Directive = Directive
+    { name :: Name
+    , arguments :: [Argument]
+    , location :: Location
+    } deriving (Eq, Show)
+
+-- * Type System
+
+-- | Type system can define a schema, a type or a directive.
+--
+-- @
+-- schema {
+--   query: Query
+-- }
+--
+-- directive @example on FIELD_DEFINITION
+--
+-- type Query {
+--   field: String @example
+-- }
+-- @
+--
+-- This example defines a custom directive "@example", which is applied to a
+-- field definition of the type definition "Query". On the top the schema
+-- is defined by taking advantage of the type "Query".
+data TypeSystemDefinition
+    = SchemaDefinition [Directive] (NonEmpty OperationTypeDefinition)
+    | TypeDefinition TypeDefinition
+    | DirectiveDefinition
+        Description Name ArgumentsDefinition Bool (NonEmpty DirectiveLocation)
+    deriving (Eq, Show)
+
+-- ** Type System Extensions
+
+-- | Extension for a type system definition. Only schema and type definitions
+-- can be extended.
+data TypeSystemExtension
+    = SchemaExtension SchemaExtension
+    | TypeExtension TypeExtension
+    deriving (Eq, Show)
+
+-- ** Schema
+
+-- | Root operation type definition.
+--
+-- Defining root operation types is not required since they have defaults. So
+-- the default query root type is "Query", and the default mutation root type
+-- is "Mutation". But these defaults can be changed for a specific schema. In
+-- the following code the query root type is changed to "MyQueryRootType", and
+-- the mutation root type to "MyMutationRootType":
+--
+-- @
+-- schema {
+--   query: MyQueryRootType
+--   mutation: MyMutationRootType
+-- }
+-- @
+data OperationTypeDefinition
+    = OperationTypeDefinition OperationType NamedType
+    deriving (Eq, Show)
+
+-- | Extension of the schema definition by further operations or directives.
+data SchemaExtension
+    = SchemaOperationExtension [Directive] (NonEmpty OperationTypeDefinition)
+    | SchemaDirectivesExtension (NonEmpty Directive)
+    deriving (Eq, Show)
+
+-- ** Descriptions
+
+-- | GraphQL has built-in capability to document service APIs. Documentation
+-- is a GraphQL string that precedes a particular definition and contains
+-- Markdown. Any GraphQL definition can be documented this way.
+--
+-- @
+-- """
+-- Supported languages.
+-- """
+-- enum Language {
+--   "English"
+--   EN
+--
+--   "Russian"
+--   RU
+-- }
+-- @
+newtype Description = Description (Maybe Text)
+    deriving (Eq, Show)
+
+instance Semigroup Description
+  where
+    Description lhs <> Description rhs = Description $ lhs <> rhs
+
+instance Monoid Description
+  where
+    mempty = Description mempty
+
+-- ** Types
+
+-- | Type definitions describe various user-defined types.
+data TypeDefinition
+    = ScalarTypeDefinition Description Name [Directive]
+    | ObjectTypeDefinition
+        Description Name (ImplementsInterfaces []) [Directive] [FieldDefinition]
+    | InterfaceTypeDefinition
+        Description Name (ImplementsInterfaces []) [Directive] [FieldDefinition]
+    | UnionTypeDefinition Description Name [Directive] (UnionMemberTypes [])
+    | EnumTypeDefinition Description Name [Directive] [EnumValueDefinition]
+    | InputObjectTypeDefinition
+        Description Name [Directive] [InputValueDefinition]
+    deriving (Eq, Show)
+
+-- | Extensions for custom, already defined types.
+data TypeExtension
+    = ScalarTypeExtension Name (NonEmpty Directive)
+    | ObjectTypeFieldsDefinitionExtension
+        Name (ImplementsInterfaces []) [Directive] (NonEmpty FieldDefinition)
+    | ObjectTypeDirectivesExtension
+        Name (ImplementsInterfaces []) (NonEmpty Directive)
+    | ObjectTypeImplementsInterfacesExtension
+        Name (ImplementsInterfaces NonEmpty)
+    | InterfaceTypeFieldsDefinitionExtension
+        Name [Directive] (NonEmpty FieldDefinition)
+    | InterfaceTypeDirectivesExtension Name (NonEmpty Directive)
+    | UnionTypeUnionMemberTypesExtension
+        Name [Directive] (UnionMemberTypes NonEmpty)
+    | UnionTypeDirectivesExtension Name (NonEmpty Directive)
+    | EnumTypeEnumValuesDefinitionExtension
+        Name [Directive] (NonEmpty EnumValueDefinition)
+    | EnumTypeDirectivesExtension Name (NonEmpty Directive)
+    | InputObjectTypeInputFieldsDefinitionExtension
+        Name [Directive] (NonEmpty InputValueDefinition)
+    | InputObjectTypeDirectivesExtension Name (NonEmpty Directive)
+    deriving (Eq, Show)
+
+-- ** Objects
+
+-- | Defines a list of interfaces implemented by the given object type.
+--
+-- @
+-- type Business implements NamedEntity & ValuedEntity {
+--   name: String
+-- }
+-- @
+--
+-- Here the object type "Business" implements two interfaces: "NamedEntity" and
+-- "ValuedEntity".
+newtype ImplementsInterfaces t = ImplementsInterfaces (t NamedType)
+
+instance Foldable t => Eq (ImplementsInterfaces t) where
+    (ImplementsInterfaces xs) == (ImplementsInterfaces ys)
+        = toList xs == toList ys
+
+instance Foldable t => Show (ImplementsInterfaces t) where
+    show (ImplementsInterfaces interfaces) = Text.unpack
+        $ Text.append "implements"
+        $ Text.intercalate " & "
+        $ toList interfaces
+
+-- | Definition of a single field in a type.
+--
+-- @
+-- type Person {
+--   name: String
+--   picture(width: Int, height: Int): Url
+-- }
+-- @
+--
+-- "name" and "picture", including their arguments and types, are field
+-- definitions.
+data FieldDefinition
+    = FieldDefinition Description Name ArgumentsDefinition Type [Directive]
+    deriving (Eq, Show)
+
+-- | A list of values passed to a field.
+--
+-- @
+-- type Person {
+--   name: String
+--   picture(width: Int, height: Int): Url
+-- }
+-- @
+--
+-- "Person" has two fields, "name" and "picture". "name" doesn't have any
+-- arguments, so 'ArgumentsDefinition' contains an empty list. "picture"
+-- contains definitions for 2 arguments: "width" and "height".
+newtype ArgumentsDefinition = ArgumentsDefinition [InputValueDefinition]
+    deriving (Eq, Show)
+
+instance Semigroup ArgumentsDefinition where
+    (ArgumentsDefinition xs) <> (ArgumentsDefinition ys) =
+        ArgumentsDefinition $ xs <> ys
+
+instance Monoid ArgumentsDefinition where
+    mempty = ArgumentsDefinition []
+
+-- | Defines an input value.
+--
+-- * Input values can define field arguments, see 'ArgumentsDefinition'.
+-- * They can also be used as field definitions in an input type.
+--
+-- @
+-- input Point2D {
+--   x: Float
+--   y: Float
+-- }
+-- @
+--
+-- The input type "Point2D" contains two value definitions: "x" and "y".
+data InputValueDefinition = InputValueDefinition
+    Description Name Type (Maybe (Node ConstValue)) [Directive]
+    deriving (Eq, Show)
+
+-- ** Unions
+
+-- | List of types forming a union.
+--
+-- @
+-- union SearchResult = Person | Photo
+-- @
+--
+-- "Person" and "Photo" are member types of the union "SearchResult".
+newtype UnionMemberTypes t = UnionMemberTypes (t NamedType)
+
+instance Foldable t => Eq (UnionMemberTypes t) where
+    (UnionMemberTypes xs) == (UnionMemberTypes ys) = toList xs == toList ys
+
+instance Foldable t => Show (UnionMemberTypes t) where
+    show (UnionMemberTypes memberTypes) = Text.unpack
+        $ Text.intercalate " | "
+        $ toList memberTypes
+
+-- ** Enums
+
+-- | Single value in an enum definition.
+--
+-- @
+-- enum Direction {
+--   NORTH
+--   EAST
+--   SOUTH
+--   WEST
+-- }
+-- @
+--
+-- "NORTH, "EAST", "SOUTH", and "WEST" are value definitions of an enum type
+-- definition "Direction".
+data EnumValueDefinition = EnumValueDefinition Description Name [Directive]
+    deriving (Eq, Show)

src/Language/GraphQL/AST/Encoder.hs

@@ -0,0 +1,597 @@
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE Safe #-}
+
+-- | This module defines a minifier and a printer for the @GraphQL@ language.
+module Language.GraphQL.AST.Encoder
+    ( Formatter
+    , definition
+    , directive
+    , document
+    , minified
+    , operationType
+    , pretty
+    , type'
+    , typeSystemDefinition
+    , value
+    ) where
+
+import Data.Foldable (fold, Foldable (..))
+import qualified Data.List.NonEmpty as NonEmpty
+import Data.Text (Text)
+import qualified Data.Text as Text
+import qualified Data.Text.Lazy as Lazy (Text)
+import qualified Data.Text.Lazy as Lazy.Text
+import Data.Text.Lazy.Builder (Builder)
+import qualified Data.Text.Lazy.Builder as Builder
+import Data.Text.Lazy.Builder.Int (decimal)
+import Data.Text.Lazy.Builder.RealFloat (realFloat)
+import qualified Language.GraphQL.AST.Document as Full
+import qualified Language.GraphQL.AST.DirectiveLocation as DirectiveLocation
+
+-- | Instructs the encoder whether the GraphQL document should be minified or
+--   pretty printed.
+--
+--   Use 'pretty' or 'minified' to construct the formatter.
+data Formatter
+    = Minified
+    | Pretty !Word
+
+-- | Constructs a formatter for pretty printing.
+pretty :: Formatter
+pretty = Pretty 0
+
+-- | Constructs a formatter for minifying.
+minified :: Formatter
+minified = Minified
+
+-- | Converts a Document' into a string.
+document :: Formatter -> Full.Document -> Lazy.Text
+document formatter defs
+    | Pretty _ <- formatter = Lazy.Text.intercalate "\n" encodeDocument
+    | Minified <-formatter = Lazy.Text.snoc (mconcat encodeDocument) '\n'
+  where
+    encodeDocument = foldr executableDefinition [] defs
+    executableDefinition (Full.ExecutableDefinition executableDefinition') acc =
+        definition formatter executableDefinition' : acc
+    executableDefinition (Full.TypeSystemDefinition typeSystemDefinition' _location) acc =
+        typeSystemDefinition formatter typeSystemDefinition' : acc
+    executableDefinition (Full.TypeSystemExtension typeSystemExtension' _location) acc =
+        typeSystemExtension formatter typeSystemExtension' : acc
+
+directiveLocation :: DirectiveLocation.DirectiveLocation -> Lazy.Text
+directiveLocation = Lazy.Text.pack . show
+
+withLineBreak :: Formatter -> Lazy.Text.Text -> Lazy.Text.Text
+withLineBreak formatter encodeDefinition
+    | Pretty _ <- formatter = Lazy.Text.snoc encodeDefinition '\n'
+    | Minified <- formatter = encodeDefinition
+
+typeSystemExtension :: Formatter -> Full.TypeSystemExtension -> Lazy.Text
+typeSystemExtension formatter = \case
+    Full.SchemaExtension schemaExtension' ->
+        schemaExtension formatter schemaExtension'
+    Full.TypeExtension typeExtension' -> typeExtension formatter typeExtension'
+
+schemaExtension :: Formatter -> Full.SchemaExtension -> Lazy.Text
+schemaExtension formatter = \case
+    Full.SchemaOperationExtension operationDirectives operationTypeDefinitions' ->
+        withLineBreak formatter
+            $ "extend schema "
+            <> optempty (directives formatter) operationDirectives
+            <> bracesList formatter (operationTypeDefinition formatter) (NonEmpty.toList operationTypeDefinitions')
+    Full.SchemaDirectivesExtension operationDirectives -> "extend schema "
+        <> optempty (directives formatter) (NonEmpty.toList operationDirectives)
+
+typeExtension :: Formatter -> Full.TypeExtension -> Lazy.Text
+typeExtension formatter = \case
+    Full.ScalarTypeExtension name' directives'
+        -> "extend scalar "
+        <> Lazy.Text.fromStrict name'
+        <> directives formatter (NonEmpty.toList directives')
+    Full.ObjectTypeFieldsDefinitionExtension name' ifaces' directives' fields'
+        -> "extend type "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (" " <>) (implementsInterfaces ifaces')
+        <> optempty (directives formatter) directives'
+        <> eitherFormat formatter " " ""
+        <> bracesList formatter (fieldDefinition nextFormatter) (NonEmpty.toList fields')
+    Full.ObjectTypeDirectivesExtension name' ifaces' directives'
+        -> "extend type "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (" " <>) (implementsInterfaces ifaces')
+        <> optempty (directives formatter) (NonEmpty.toList directives')
+    Full.ObjectTypeImplementsInterfacesExtension name' ifaces'
+        -> "extend type "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (" " <>) (implementsInterfaces ifaces')
+    Full.InterfaceTypeFieldsDefinitionExtension name' directives' fields'
+        -> "extend interface "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) directives'
+        <> eitherFormat formatter " " ""
+        <> bracesList formatter (fieldDefinition nextFormatter) (NonEmpty.toList fields')
+    Full.InterfaceTypeDirectivesExtension name' directives'
+        -> "extend interface "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) (NonEmpty.toList directives')
+    Full.UnionTypeUnionMemberTypesExtension name' directives' members'
+        -> "extend union "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) directives'
+        <> eitherFormat formatter " " ""
+        <> unionMemberTypes formatter members'
+    Full.UnionTypeDirectivesExtension name' directives'
+        -> "extend union "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) (NonEmpty.toList directives')
+    Full.EnumTypeEnumValuesDefinitionExtension name' directives' members'
+        -> "extend enum "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) directives'
+        <> eitherFormat formatter " " ""
+        <> bracesList formatter (enumValueDefinition formatter) (NonEmpty.toList members')
+    Full.EnumTypeDirectivesExtension name' directives'
+        -> "extend enum "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) (NonEmpty.toList directives')
+    Full.InputObjectTypeInputFieldsDefinitionExtension name' directives' fields'
+        -> "extend input "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) directives'
+        <> eitherFormat formatter " " ""
+        <> bracesList formatter (inputValueDefinition nextFormatter) (NonEmpty.toList fields')
+    Full.InputObjectTypeDirectivesExtension name' directives'
+        -> "extend input "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) (NonEmpty.toList directives')
+  where
+    nextFormatter = incrementIndent formatter
+
+-- | Converts a t'Full.TypeSystemDefinition' into a string.
+typeSystemDefinition :: Formatter -> Full.TypeSystemDefinition -> Lazy.Text
+typeSystemDefinition formatter = \case
+    Full.SchemaDefinition operationDirectives operationTypeDefinitions' ->
+        withLineBreak formatter
+            $ "schema "
+            <> optempty (directives formatter) operationDirectives
+            <> bracesList formatter (operationTypeDefinition formatter) (NonEmpty.toList operationTypeDefinitions')
+    Full.TypeDefinition typeDefinition' -> typeDefinition formatter typeDefinition'
+    Full.DirectiveDefinition description' name' arguments' repeatable locations
+        -> description formatter description'
+        <> "@"
+        <> Lazy.Text.fromStrict name'
+        <> argumentsDefinition formatter arguments'
+        <> (if repeatable then " repeatable" else mempty)
+        <> " on"
+        <> pipeList formatter (directiveLocation <$> locations)
+
+operationTypeDefinition :: Formatter -> Full.OperationTypeDefinition -> Lazy.Text.Text
+operationTypeDefinition formatter (Full.OperationTypeDefinition operationType' namedType')
+    = indentLine (incrementIndent formatter)
+    <> operationType formatter operationType'
+    <> colon formatter
+    <> Lazy.Text.fromStrict namedType'
+
+fieldDefinition :: Formatter -> Full.FieldDefinition -> Lazy.Text.Text
+fieldDefinition formatter fieldDefinition' =
+    let Full.FieldDefinition description' name' arguments' type'' directives' = fieldDefinition'
+     in optempty (description formatter) description'
+            <> indentLine formatter
+            <> Lazy.Text.fromStrict name'
+            <> argumentsDefinition formatter arguments'
+            <> colon formatter
+            <> type' type''
+            <> optempty (directives formatter) directives'
+
+argumentsDefinition :: Formatter -> Full.ArgumentsDefinition -> Lazy.Text.Text
+argumentsDefinition formatter (Full.ArgumentsDefinition arguments') =
+    parensCommas formatter (argumentDefinition formatter) arguments'
+
+argumentDefinition :: Formatter -> Full.InputValueDefinition -> Lazy.Text.Text
+argumentDefinition formatter definition' =
+    let Full.InputValueDefinition description' name' type'' defaultValue' directives' = definition'
+     in optempty (description formatter) description'
+            <> Lazy.Text.fromStrict name'
+            <> colon formatter
+            <> type' type''
+            <> maybe mempty (defaultValue formatter . Full.node) defaultValue'
+            <> directives formatter directives'
+
+inputValueDefinition :: Formatter -> Full.InputValueDefinition -> Lazy.Text.Text
+inputValueDefinition formatter definition' =
+    let Full.InputValueDefinition description' name' type'' defaultValue' directives' = definition'
+     in optempty (description formatter) description'
+            <> indentLine formatter
+            <> Lazy.Text.fromStrict name'
+            <> colon formatter
+            <> type' type''
+            <> maybe mempty (defaultValue formatter . Full.node) defaultValue'
+            <> directives formatter directives'
+
+typeDefinition :: Formatter -> Full.TypeDefinition -> Lazy.Text
+typeDefinition formatter = \case
+    Full.ScalarTypeDefinition description' name' directives'
+        -> optempty (description formatter) description'
+        <> "scalar "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) directives'
+    Full.ObjectTypeDefinition description' name' ifaces' directives' fields'
+        -> optempty (description formatter) description'
+        <> "type "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (" " <>) (implementsInterfaces ifaces')
+        <> optempty (directives formatter) directives'
+        <> eitherFormat formatter " " ""
+        <> bracesList formatter (fieldDefinition nextFormatter) fields'
+    Full.InterfaceTypeDefinition description' name' ifaces' directives' fields'
+        -> optempty (description formatter) description'
+        <> "interface "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (" " <>) (implementsInterfaces ifaces')
+        <> optempty (directives formatter) directives'
+        <> eitherFormat formatter " " ""
+        <> bracesList formatter (fieldDefinition nextFormatter) fields'
+    Full.UnionTypeDefinition description' name' directives' members'
+        -> optempty (description formatter) description'
+        <> "union "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) directives'
+        <> eitherFormat formatter " " ""
+        <> unionMemberTypes formatter members'
+    Full.EnumTypeDefinition description' name' directives' members'
+        -> optempty (description formatter) description'
+        <> "enum "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) directives'
+        <> eitherFormat formatter " " ""
+        <> bracesList formatter (enumValueDefinition formatter) members'
+    Full.InputObjectTypeDefinition description' name' directives' fields'
+        -> optempty (description formatter) description'
+        <> "input "
+        <> Lazy.Text.fromStrict name'
+        <> optempty (directives formatter) directives'
+        <> eitherFormat formatter " " ""
+        <> bracesList formatter (inputValueDefinition nextFormatter) fields'
+  where
+    nextFormatter = incrementIndent formatter
+
+implementsInterfaces :: Foldable t => Full.ImplementsInterfaces t -> Lazy.Text
+implementsInterfaces (Full.ImplementsInterfaces interfaces)
+    | null interfaces = mempty
+    | otherwise = Lazy.Text.fromStrict
+        $ Text.append "implements "
+        $ Text.intercalate " & "
+        $ toList interfaces
+
+unionMemberTypes :: Foldable t => Formatter -> Full.UnionMemberTypes t -> Lazy.Text
+unionMemberTypes formatter (Full.UnionMemberTypes memberTypes)
+    | null memberTypes = mempty
+    | otherwise = Lazy.Text.append "="
+        $ pipeList formatter
+        $ Lazy.Text.fromStrict
+        <$> toList memberTypes
+
+pipeList :: Foldable t => Formatter -> t Lazy.Text -> Lazy.Text
+pipeList Minified =  (" " <>) . Lazy.Text.intercalate " | " . toList
+pipeList (Pretty _) =  Lazy.Text.concat
+    . fmap (("\n" <> indentSymbol <> "| ") <>)
+    . toList
+
+enumValueDefinition :: Formatter -> Full.EnumValueDefinition -> Lazy.Text
+enumValueDefinition (Pretty _) enumValue =
+    let Full.EnumValueDefinition description' name' directives' = enumValue
+        formatter = Pretty 1
+     in description formatter description'
+        <> indentLine formatter
+        <> Lazy.Text.fromStrict name'
+        <> directives formatter directives'
+enumValueDefinition Minified enumValue =
+    let Full.EnumValueDefinition description' name' directives' = enumValue
+     in description Minified description'
+        <> Lazy.Text.fromStrict name'
+        <> directives Minified directives'
+
+description :: Formatter -> Full.Description -> Lazy.Text.Text
+description _formatter (Full.Description Nothing) = ""
+description formatter (Full.Description (Just description')) =
+    stringValue formatter description'
+
+-- | Converts a t'Full.ExecutableDefinition' into a string.
+definition :: Formatter -> Full.ExecutableDefinition -> Lazy.Text
+definition formatter x
+    | Pretty _ <- formatter = Lazy.Text.snoc (encodeDefinition x) '\n'
+    | Minified <- formatter = encodeDefinition x
+  where
+    encodeDefinition (Full.DefinitionOperation operation)
+        = operationDefinition formatter operation
+    encodeDefinition (Full.DefinitionFragment fragment)
+        = fragmentDefinition formatter fragment
+
+-- | Converts a 'Full.OperationDefinition into a string.
+operationDefinition :: Formatter -> Full.OperationDefinition -> Lazy.Text
+operationDefinition formatter = \case
+    Full.SelectionSet sels _ -> selectionSet formatter sels
+    Full.OperationDefinition Full.Query name vars dirs sels _ ->
+        "query " <> root name vars dirs sels
+    Full.OperationDefinition Full.Mutation name vars dirs sels _ ->
+        "mutation " <> root name vars dirs sels
+    Full.OperationDefinition Full.Subscription name vars dirs sels _ ->
+        "subscription " <> root name vars dirs sels
+  where
+    -- | Converts a Query or Mutation into a string.
+    root :: Maybe Full.Name ->
+        [Full.VariableDefinition] ->
+        [Full.Directive] ->
+        Full.SelectionSet ->
+        Lazy.Text
+    root name vars dirs sels
+        = Lazy.Text.fromStrict (fold name)
+        <> optempty (variableDefinitions formatter) vars
+        <> optempty (directives formatter) dirs
+        <> eitherFormat formatter " " mempty
+        <> selectionSet formatter sels
+
+variableDefinitions :: Formatter -> [Full.VariableDefinition] -> Lazy.Text
+variableDefinitions formatter
+    = parensCommas formatter $ variableDefinition formatter
+
+variableDefinition :: Formatter -> Full.VariableDefinition -> Lazy.Text
+variableDefinition formatter variableDefinition' =
+    let Full.VariableDefinition variableName variableType defaultValue' _ =
+            variableDefinition'
+     in variable variableName
+    <> colon formatter
+    <> type' variableType
+    <> maybe mempty (defaultValue formatter . Full.node) defaultValue'
+
+defaultValue :: Formatter -> Full.ConstValue -> Lazy.Text
+defaultValue formatter val
+    = eitherFormat formatter " = " "="
+    <> value formatter (fromConstValue val)
+
+variable :: Full.Name -> Lazy.Text
+variable var = "$" <> Lazy.Text.fromStrict var
+
+selectionSet :: Formatter -> Full.SelectionSet -> Lazy.Text
+selectionSet formatter
+    = bracesList formatter (selection formatter)
+    . NonEmpty.toList
+
+selectionSetOpt :: Formatter -> Full.SelectionSetOpt -> Lazy.Text
+selectionSetOpt formatter = bracesList formatter $ selection formatter
+
+indentSymbol :: Lazy.Text
+indentSymbol = "  "
+
+indent :: (Integral a) => a -> Lazy.Text
+indent indentation = Lazy.Text.replicate (fromIntegral indentation) indentSymbol
+
+selection :: Formatter -> Full.Selection -> Lazy.Text
+selection formatter = Lazy.Text.append (indentLine formatter')
+    . encodeSelection
+  where
+    encodeSelection (Full.FieldSelection fieldSelection) =
+        field formatter' fieldSelection
+    encodeSelection (Full.InlineFragmentSelection fragmentSelection) =
+        inlineFragment formatter' fragmentSelection
+    encodeSelection (Full.FragmentSpreadSelection fragmentSelection) =
+        fragmentSpread formatter' fragmentSelection
+    formatter' = incrementIndent formatter
+
+indentLine :: Formatter -> Lazy.Text
+indentLine formatter
+    | Pretty indentation <- formatter = indent indentation
+    | otherwise = ""
+
+incrementIndent :: Formatter -> Formatter
+incrementIndent formatter
+    | Pretty indentation <- formatter = Pretty $ indentation + 1
+    | otherwise = Minified
+
+colon :: Formatter -> Lazy.Text
+colon formatter = eitherFormat formatter ": " ":"
+
+-- | Converts Field into a string.
+field :: Formatter -> Full.Field -> Lazy.Text
+field formatter (Full.Field alias name args dirs set _)
+    = optempty prependAlias (fold alias)
+    <> Lazy.Text.fromStrict name
+    <> optempty (arguments formatter) args
+    <> optempty (directives formatter) dirs
+    <> optempty selectionSetOpt' set
+  where
+    prependAlias aliasName = Lazy.Text.fromStrict aliasName <>  colon formatter
+    selectionSetOpt' = (eitherFormat formatter " " "" <>)
+        . selectionSetOpt formatter
+
+arguments :: Formatter -> [Full.Argument] -> Lazy.Text
+arguments formatter = parensCommas formatter $ argument formatter
+
+argument :: Formatter -> Full.Argument -> Lazy.Text
+argument formatter (Full.Argument name value' _)
+    = Lazy.Text.fromStrict name
+    <> colon formatter
+    <> value formatter (Full.node value')
+
+-- * Fragments
+
+fragmentSpread :: Formatter -> Full.FragmentSpread -> Lazy.Text
+fragmentSpread formatter (Full.FragmentSpread name directives' _)
+    = "..." <> Lazy.Text.fromStrict name
+    <> optempty (directives formatter) directives'
+
+inlineFragment :: Formatter -> Full.InlineFragment -> Lazy.Text
+inlineFragment formatter (Full.InlineFragment typeCondition directives' selections _)
+    = "... on "
+    <> Lazy.Text.fromStrict (fold typeCondition)
+    <> directives formatter directives'
+    <> eitherFormat formatter " " mempty
+    <> selectionSet formatter selections
+
+fragmentDefinition :: Formatter -> Full.FragmentDefinition -> Lazy.Text
+fragmentDefinition formatter (Full.FragmentDefinition name tc dirs sels _)
+    = "fragment " <> Lazy.Text.fromStrict name
+    <> " on " <> Lazy.Text.fromStrict tc
+    <> optempty (directives formatter) dirs
+    <> eitherFormat formatter " " mempty
+    <> selectionSet formatter sels
+
+-- * Miscellaneous
+
+-- | Converts a 'Full.Directive' into a string.
+directive :: Formatter -> Full.Directive -> Lazy.Text
+directive formatter (Full.Directive name args _)
+    = "@" <> Lazy.Text.fromStrict name <> optempty (arguments formatter) args
+
+directives :: Formatter -> [Full.Directive] -> Lazy.Text
+directives Minified values = spaces (directive Minified) values
+directives formatter values
+    | null values = ""
+    | otherwise = Lazy.Text.cons ' ' $ spaces (directive formatter) values
+
+-- | Converts a 'Full.Value' into a string.
+value :: Formatter -> Full.Value -> Lazy.Text
+value _ (Full.Variable x) = variable x
+value _ (Full.Int x) = Builder.toLazyText $ decimal x
+value _ (Full.Float x) = Builder.toLazyText $ realFloat x
+value _ (Full.Boolean  x) = booleanValue x
+value _ Full.Null = "null"
+value formatter (Full.String string) = stringValue formatter string
+value _ (Full.Enum x) = Lazy.Text.fromStrict x
+value formatter (Full.List x) = listValue formatter x
+value formatter (Full.Object x) = objectValue formatter x
+
+fromConstValue :: Full.ConstValue -> Full.Value
+fromConstValue (Full.ConstInt x) = Full.Int x
+fromConstValue (Full.ConstFloat x) = Full.Float x
+fromConstValue (Full.ConstBoolean  x) = Full.Boolean x
+fromConstValue Full.ConstNull = Full.Null
+fromConstValue (Full.ConstString string) = Full.String string
+fromConstValue (Full.ConstEnum x) = Full.Enum x
+fromConstValue (Full.ConstList x) = Full.List $ fmap fromConstValue <$> x
+fromConstValue (Full.ConstObject x) = Full.Object $ fromConstObjectField <$> x
+  where
+    fromConstObjectField Full.ObjectField{value = value', ..} =
+        Full.ObjectField name (fromConstValue <$> value') location
+
+booleanValue :: Bool -> Lazy.Text
+booleanValue True  = "true"
+booleanValue False = "false"
+
+quote :: Builder.Builder
+quote = Builder.singleton '\"'
+
+oneLine :: Text -> Builder
+oneLine string = quote <> Text.foldr merge quote string
+  where
+    merge = mappend . Builder.fromString . Full.escape
+
+stringValue :: Formatter -> Text -> Lazy.Text
+stringValue Minified string = Builder.toLazyText $ oneLine string
+stringValue (Pretty indentation) string =
+  if hasEscaped string
+  then stringValue Minified string
+  else Builder.toLazyText $ encoded lines'
+    where
+      isWhiteSpace char = char == ' ' || char == '\t'
+      isNewline char = char == '\n' || char == '\r'
+      hasEscaped = Text.any (not . isAllowed)
+      isAllowed char =
+          char == '\t' || isNewline char || (char >= '\x0020' && char /= '\x007F')
+
+      tripleQuote = Builder.fromText "\"\"\""
+      newline = Builder.singleton '\n'
+
+      strip = Text.dropWhile isWhiteSpace . Text.dropWhileEnd isWhiteSpace
+      lines' = map Builder.fromText $ Text.split isNewline (Text.replace "\r\n" "\n" $ strip string)
+      encoded [] = oneLine string
+      encoded [_] = oneLine string
+      encoded lines'' = tripleQuote <> newline
+        <> transformLines lines''
+        <> Builder.fromLazyText (indent indentation) <> tripleQuote
+      transformLines = foldr transformLine mempty
+      transformLine "" acc = newline <> acc
+      transformLine line' acc
+            = Builder.fromLazyText (indent (indentation + 1))
+            <> line' <> newline <> acc
+
+listValue :: Formatter -> [Full.Node Full.Value] -> Lazy.Text
+listValue formatter = bracketsCommas formatter $ value formatter . Full.node
+
+objectValue :: Formatter -> [Full.ObjectField Full.Value] -> Lazy.Text
+objectValue formatter = intercalate $ objectField formatter
+  where
+    intercalate f
+        = braces
+        . Lazy.Text.intercalate (eitherFormat formatter ", " ",")
+        . fmap f
+
+objectField :: Formatter -> Full.ObjectField Full.Value -> Lazy.Text
+objectField formatter (Full.ObjectField name (Full.Node value' _) _) =
+    Lazy.Text.fromStrict name <> colon formatter <> value formatter value'
+
+-- | Converts a 'Full.Type' a type into a string.
+type' :: Full.Type -> Lazy.Text
+type' (Full.TypeNamed x) = Lazy.Text.fromStrict x
+type' (Full.TypeList x) = listType x
+type' (Full.TypeNonNull x) = nonNullType x
+
+listType :: Full.Type -> Lazy.Text
+listType x = brackets (type' x)
+
+nonNullType :: Full.NonNullType -> Lazy.Text
+nonNullType (Full.NonNullTypeNamed x) = Lazy.Text.fromStrict x <> "!"
+nonNullType (Full.NonNullTypeList x) = listType x <> "!"
+
+-- | Produces lowercase operation type: query, mutation or subscription.
+operationType :: Formatter -> Full.OperationType -> Lazy.Text
+operationType _formatter Full.Query = "query"
+operationType _formatter Full.Mutation = "mutation"
+operationType _formatter Full.Subscription = "subscription"
+
+-- * Internal
+
+between :: Char -> Char -> Lazy.Text -> Lazy.Text
+between open close = Lazy.Text.cons open . (`Lazy.Text.snoc` close)
+
+parens :: Lazy.Text -> Lazy.Text
+parens = between '(' ')'
+
+brackets :: Lazy.Text -> Lazy.Text
+brackets = between '[' ']'
+
+braces :: Lazy.Text -> Lazy.Text
+braces = between '{' '}'
+
+spaces :: forall a. (a -> Lazy.Text) -> [a] -> Lazy.Text
+spaces f = Lazy.Text.intercalate "\SP" . fmap f
+
+parensCommas :: forall a. Formatter -> (a -> Lazy.Text) -> [a] -> Lazy.Text
+parensCommas formatter f
+    = parens
+    . Lazy.Text.intercalate (eitherFormat formatter ", " ",")
+    . fmap f
+
+bracketsCommas :: Formatter -> (a -> Lazy.Text) -> [a] -> Lazy.Text
+bracketsCommas formatter f
+    = brackets
+    . Lazy.Text.intercalate (eitherFormat formatter ", " ",")
+    . fmap f
+
+bracesList :: forall a. Formatter -> (a -> Lazy.Text) -> [a] -> Lazy.Text
+bracesList (Pretty intendation) f xs
+    = Lazy.Text.snoc (Lazy.Text.intercalate "\n" content) '\n'
+    <> (Lazy.Text.snoc $ Lazy.Text.replicate (fromIntegral intendation) "  ") '}'
+  where
+    content = "{" : fmap f xs
+bracesList Minified f xs = braces $ Lazy.Text.intercalate "," $ fmap f xs
+
+optempty :: (Eq a, Monoid a, Monoid b) => (a -> b) -> a -> b
+optempty f xs = if xs == mempty then mempty else f xs
+
+eitherFormat :: forall a. Formatter -> a -> a -> a
+eitherFormat (Pretty _) x _ = x
+eitherFormat Minified _ x = x

src/Language/GraphQL/AST/Lexer.hs

@@ -0,0 +1,239 @@
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+-- | This module defines a bunch of small parsers used to parse individual
+--   lexemes.
+module Language.GraphQL.AST.Lexer
+    ( Parser
+    , amp
+    , at
+    , bang
+    , blockString
+    , braces
+    , brackets
+    , colon
+    , dollar
+    , comment
+    , equals
+    , extend
+    , integer
+    , float
+    , lexeme
+    , name
+    , parens
+    , pipe
+    , spaceConsumer
+    , spread
+    , string
+    , symbol
+    , unicodeBOM
+    ) where
+
+import Control.Applicative (Alternative(..))
+import qualified Control.Applicative.Combinators.NonEmpty as NonEmpty
+import Data.Char (chr, digitToInt, isAsciiLower, isAsciiUpper, ord)
+import Data.Foldable (foldl')
+import Data.List (dropWhileEnd)
+import qualified Data.List.NonEmpty as NonEmpty
+import Data.List.NonEmpty (NonEmpty(..))
+import Data.Proxy (Proxy(..))
+import Data.Void (Void)
+import Text.Megaparsec
+    ( Parsec
+    , (<?>)
+    , between
+    , chunk
+    , chunkToTokens
+    , notFollowedBy
+    , oneOf
+    , option
+    , optional
+    , satisfy
+    , skipSome
+    , takeP
+    , takeWhile1P
+    , try
+    )
+import Text.Megaparsec.Char (char, digitChar, space1)
+import qualified Text.Megaparsec.Char.Lexer as Lexer
+import Data.Text (Text)
+import qualified Data.Text as T
+import qualified Data.Text.Lazy as TL
+import Control.Monad (void)
+
+-- | Standard parser.
+-- Accepts the type of the parsed token.
+type Parser = Parsec Void T.Text
+
+ignoredCharacters :: Parser ()
+ignoredCharacters = space1 <|> skipSome (char ',')
+
+-- | Parser that skips comments and meaningless characters, whitespaces and
+-- commas.
+spaceConsumer :: Parser ()
+spaceConsumer = Lexer.space ignoredCharacters comment empty
+
+-- | Parser for comments.
+comment :: Parser ()
+comment = Lexer.skipLineComment "#"
+
+-- | Lexeme definition which ignores whitespaces and commas.
+lexeme :: forall a. Parser a -> Parser a
+lexeme = Lexer.lexeme spaceConsumer
+
+-- | Symbol definition which ignores whitespaces and commas.
+symbol :: T.Text -> Parser T.Text
+symbol = Lexer.symbol spaceConsumer
+
+-- | Parser for "!".
+bang :: Parser T.Text
+bang = symbol "!"
+
+-- | Parser for "$".
+dollar :: Parser T.Text
+dollar = symbol "$"
+
+-- | Parser for "@".
+at :: Parser ()
+at = void $ symbol "@"
+
+-- | Parser for "&".
+amp :: Parser T.Text
+amp = symbol "&"
+
+-- | Parser for ":".
+colon :: Parser ()
+colon = void $ symbol ":"
+
+-- | Parser for "=".
+equals :: Parser T.Text
+equals = symbol "="
+
+-- | Parser for the spread operator (...).
+spread :: Parser T.Text
+spread = symbol "..."
+
+-- | Parser for "|".
+pipe :: Parser T.Text
+pipe = symbol "|"
+
+-- | Parser for an expression between "(" and ")".
+parens :: forall a. Parser a -> Parser a
+parens = between (symbol "(") (symbol ")")
+
+-- | Parser for an expression between "[" and "]".
+brackets :: forall a. Parser a -> Parser a
+brackets = between (symbol "[") (symbol "]")
+
+-- | Parser for an expression between "{" and "}".
+braces :: forall a. Parser a -> Parser a
+braces = between (symbol "{") (symbol "}")
+
+-- | Parser for strings.
+string :: Parser T.Text
+string = between "\"" "\"" stringValue <* spaceConsumer
+  where
+    stringValue = T.pack <$> many stringCharacter
+    stringCharacter = satisfy isStringCharacter1
+        <|> escapeSequence
+    isStringCharacter1 = liftA2 (&&) isSourceCharacter isChunkDelimiter
+
+-- | Parser for block strings.
+blockString :: Parser T.Text
+blockString = between "\"\"\"" "\"\"\"" stringValue <* spaceConsumer
+  where
+    stringValue = do
+        byLine <- NonEmpty.sepBy1 (many blockStringCharacter) lineTerminator
+        let indentSize = foldr countIndent 0 $ NonEmpty.tail byLine
+            withoutIndent = NonEmpty.head byLine
+                : (removeIndent indentSize <$> NonEmpty.tail byLine)
+            withoutEmptyLines = liftA2 (.) dropWhile dropWhileEnd removeEmptyLine withoutIndent
+
+        pure $ T.intercalate "\n" $ T.concat <$> withoutEmptyLines
+    removeEmptyLine [] = True
+    removeEmptyLine [x] = T.null x || isWhiteSpace (T.head x)
+    removeEmptyLine _ = False
+    blockStringCharacter
+        = takeWhile1P Nothing isWhiteSpace
+        <|> takeWhile1P Nothing isBlockStringCharacter1
+        <|> escapeTripleQuote
+        <|> try (chunk "\"" <* notFollowedBy (chunk "\"\""))
+    escapeTripleQuote = chunk "\\" >>= flip option (chunk "\"\"")
+    isBlockStringCharacter1 = liftA2 (&&) isSourceCharacter isChunkDelimiter
+    countIndent [] acc = acc
+    countIndent (x:_) acc
+        | T.null x = acc
+        | not (isWhiteSpace $ T.head x) = acc
+        | acc == 0 = T.length x
+        | otherwise = min acc $ T.length x
+    removeIndent _ [] = []
+    removeIndent n (x:chunks) = T.drop n x : chunks
+
+-- | Parser for integers.
+integer :: Integral a => Parser a
+integer = Lexer.signed (pure ()) (lexeme Lexer.decimal) <?> "IntValue"
+
+-- | Parser for floating-point numbers.
+float :: Parser Double
+float = Lexer.signed (pure ()) (lexeme Lexer.float) <?> "FloatValue"
+
+-- | Parser for names (/[_A-Za-z][_0-9A-Za-z]*/).
+name :: Parser T.Text
+name = do
+    firstLetter <- nameFirstLetter
+    rest <- many $ nameFirstLetter <|> digitChar
+    void spaceConsumer
+    pure $ TL.toStrict $ TL.cons firstLetter $ TL.pack rest
+  where
+    nameFirstLetter = satisfy isAsciiUpper <|> satisfy isAsciiLower <|> char '_'
+
+isChunkDelimiter :: Char -> Bool
+isChunkDelimiter = flip notElem ['"', '\\', '\n', '\r']
+
+isWhiteSpace :: Char -> Bool
+isWhiteSpace = liftA2 (||) (== ' ') (== '\t')
+
+lineTerminator :: Parser T.Text
+lineTerminator = chunk "\r\n" <|> chunk "\n" <|> chunk "\r"
+
+isSourceCharacter :: Char -> Bool
+isSourceCharacter = isSourceCharacter' . ord
+  where
+    isSourceCharacter' code
+        = code >= 0x0020
+        || elem code [0x0009, 0x000a, 0x000d]
+
+escapeSequence :: Parser Char
+escapeSequence = do
+    void $ char '\\'
+    escaped <- oneOf ['"', '\\', '/', 'b', 'f', 'n', 'r', 't', 'u']
+    case escaped of
+        'b' -> pure '\b'
+        'f' -> pure '\f'
+        'n' -> pure '\n'
+        'r' -> pure '\r'
+        't' -> pure '\t'
+        'u' -> chr
+            . foldl' step 0
+            . chunkToTokens (Proxy :: Proxy T.Text)
+            <$> takeP Nothing 4
+        _ -> pure escaped
+  where
+    step accumulator = (accumulator * 16 +) . digitToInt
+
+-- | Parser for the "Byte Order Mark".
+unicodeBOM :: Parser ()
+unicodeBOM = void $ optional $ char '\xfeff'
+
+-- | Parses "extend" followed by a 'symbol'. It is used by schema extensions.
+extend :: forall a. Text -> String -> NonEmpty (Parser a) -> Parser a
+extend token extensionLabel parsers
+    = foldr combine headParser (NonEmpty.tail parsers)
+    <?> extensionLabel
+  where
+    headParser = tryExtension $ NonEmpty.head parsers
+    combine current accumulated = accumulated <|> tryExtension current
+    tryExtension extensionParser = try
+        $ symbol "extend"
+        *> symbol token
+        *> extensionParser

src/Language/GraphQL/AST/Parser.hs

@@ -0,0 +1,545 @@
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+
+-- | @GraphQL@ document parser.
+module Language.GraphQL.AST.Parser
+    ( document
+    ) where
+
+import Control.Applicative (Alternative(..), optional)
+import Control.Applicative.Combinators (sepBy1)
+import qualified Control.Applicative.Combinators.NonEmpty as NonEmpty
+import Data.List.NonEmpty (NonEmpty(..))
+import Data.Text (Text)
+import qualified Language.GraphQL.AST.DirectiveLocation as Directive
+import Language.GraphQL.AST.DirectiveLocation (DirectiveLocation)
+import qualified Language.GraphQL.AST.Document as Full
+import Language.GraphQL.AST.Lexer
+import Text.Megaparsec
+    ( MonadParsec(..)
+    , SourcePos(..)
+    , getSourcePos
+    , lookAhead
+    , option
+    , try
+    , unPos
+    , (<?>)
+    )
+import Data.Maybe (isJust)
+
+-- | Parser for the GraphQL documents.
+document :: Parser Full.Document
+document = unicodeBOM
+    *> spaceConsumer
+    *> lexeme (NonEmpty.some definition)
+
+definition :: Parser Full.Definition
+definition = Full.ExecutableDefinition <$> executableDefinition
+    <|> typeSystemDefinition'
+    <|> typeSystemExtension'
+    <?> "Definition"
+  where
+    typeSystemDefinition' = do
+        location <- getLocation
+        definition' <- typeSystemDefinition
+        pure $ Full.TypeSystemDefinition definition' location
+    typeSystemExtension' = do
+        location <- getLocation
+        definition' <- typeSystemExtension
+        pure $ Full.TypeSystemExtension definition' location
+
+getLocation :: Parser Full.Location
+getLocation = fromSourcePosition <$> getSourcePos
+  where
+    fromSourcePosition SourcePos{..} =
+        Full.Location (wordFromPosition sourceLine) (wordFromPosition sourceColumn)
+    wordFromPosition = fromIntegral . unPos
+
+executableDefinition :: Parser Full.ExecutableDefinition
+executableDefinition = Full.DefinitionOperation <$> operationDefinition
+    <|> Full.DefinitionFragment  <$> fragmentDefinition
+    <?> "ExecutableDefinition"
+
+typeSystemDefinition :: Parser Full.TypeSystemDefinition
+typeSystemDefinition = schemaDefinition
+    <|> typeSystemDefinitionWithDescription
+    <?> "TypeSystemDefinition"
+  where
+    typeSystemDefinitionWithDescription = description
+        >>= liftA2 (<|>) typeDefinition' directiveDefinition
+    typeDefinition' description' = Full.TypeDefinition
+        <$> typeDefinition description'
+
+typeSystemExtension :: Parser Full.TypeSystemExtension
+typeSystemExtension = Full.SchemaExtension <$> schemaExtension
+    <|> Full.TypeExtension <$> typeExtension
+    <?> "TypeSystemExtension"
+
+directiveDefinition :: Full.Description -> Parser Full.TypeSystemDefinition
+directiveDefinition description' = Full.DirectiveDefinition description'
+    <$ symbol "directive"
+    <* at
+    <*> name
+    <*> argumentsDefinition
+    <*> (isJust <$> optional (symbol "repeatable"))
+    <* symbol "on"
+    <*> directiveLocations
+    <?> "DirectiveDefinition"
+
+directiveLocations :: Parser (NonEmpty DirectiveLocation)
+directiveLocations = optional pipe
+    *> directiveLocation `NonEmpty.sepBy1` pipe
+    <?> "DirectiveLocations"
+
+directiveLocation :: Parser DirectiveLocation
+directiveLocation = e (Directive.Query <$ symbol "QUERY")
+    <|> e (Directive.Mutation <$ symbol "MUTATION")
+    <|> e (Directive.Subscription <$ symbol "SUBSCRIPTION")
+    <|> t (Directive.FieldDefinition <$ symbol "FIELD_DEFINITION")
+    <|> e (Directive.Field <$ symbol "FIELD")
+    <|> e (Directive.FragmentDefinition <$ "FRAGMENT_DEFINITION")
+    <|> e (Directive.FragmentSpread <$ "FRAGMENT_SPREAD")
+    <|> e (Directive.InlineFragment <$ "INLINE_FRAGMENT")
+    <|> t (Directive.Schema <$ symbol "SCHEMA")
+    <|> t (Directive.Scalar <$ symbol "SCALAR")
+    <|> t (Directive.Object <$ symbol "OBJECT")
+    <|> t (Directive.ArgumentDefinition <$ symbol "ARGUMENT_DEFINITION")
+    <|> t (Directive.Interface <$ symbol "INTERFACE")
+    <|> t (Directive.Union <$ symbol "UNION")
+    <|> t (Directive.EnumValue <$ symbol "ENUM_VALUE")
+    <|> t (Directive.Enum <$ symbol "ENUM")
+    <|> t (Directive.InputObject <$ symbol "INPUT_OBJECT")
+    <|> t (Directive.InputFieldDefinition <$ symbol "INPUT_FIELD_DEFINITION")
+    <?> "DirectiveLocation"
+  where
+    e = fmap Directive.ExecutableDirectiveLocation
+    t = fmap Directive.TypeSystemDirectiveLocation
+
+typeDefinition :: Full.Description -> Parser Full.TypeDefinition
+typeDefinition description' = scalarTypeDefinition description'
+    <|> objectTypeDefinition description'
+    <|> interfaceTypeDefinition description'
+    <|> unionTypeDefinition description'
+    <|> enumTypeDefinition description'
+    <|> inputObjectTypeDefinition description'
+    <?> "TypeDefinition"
+
+typeExtension :: Parser Full.TypeExtension
+typeExtension = scalarTypeExtension
+    <|> objectTypeExtension
+    <|> interfaceTypeExtension
+    <|> unionTypeExtension
+    <|> enumTypeExtension
+    <|> inputObjectTypeExtension
+    <?> "TypeExtension"
+
+scalarTypeDefinition :: Full.Description -> Parser Full.TypeDefinition
+scalarTypeDefinition description' = Full.ScalarTypeDefinition description'
+    <$ symbol "scalar"
+    <*> name
+    <*> directives
+    <?> "ScalarTypeDefinition"
+
+scalarTypeExtension :: Parser Full.TypeExtension
+scalarTypeExtension = extend "scalar" "ScalarTypeExtension"
+    $ (Full.ScalarTypeExtension <$> name <*> NonEmpty.some directive) :| []
+
+objectTypeDefinition :: Full.Description -> Parser Full.TypeDefinition
+objectTypeDefinition description' = Full.ObjectTypeDefinition description'
+    <$ symbol "type"
+    <*> name
+    <*> option (Full.ImplementsInterfaces []) (implementsInterfaces sepBy1)
+    <*> directives
+    <*> braces (many fieldDefinition)
+    <?> "ObjectTypeDefinition"
+
+objectTypeExtension :: Parser Full.TypeExtension
+objectTypeExtension = extend "type" "ObjectTypeExtension"
+    $ fieldsDefinitionExtension :|
+        [ directivesExtension
+        , implementsInterfacesExtension
+        ]
+  where
+    fieldsDefinitionExtension = Full.ObjectTypeFieldsDefinitionExtension
+        <$> name
+        <*> option (Full.ImplementsInterfaces []) (implementsInterfaces sepBy1)
+        <*> directives
+        <*> braces (NonEmpty.some fieldDefinition)
+    directivesExtension = Full.ObjectTypeDirectivesExtension
+        <$> name
+        <*> option (Full.ImplementsInterfaces []) (implementsInterfaces sepBy1)
+        <*> NonEmpty.some directive
+    implementsInterfacesExtension = Full.ObjectTypeImplementsInterfacesExtension
+        <$> name
+        <*> implementsInterfaces NonEmpty.sepBy1
+
+description :: Parser Full.Description
+description = Full.Description
+    <$> optional stringValue
+    <?> "Description"
+
+unionTypeDefinition :: Full.Description -> Parser Full.TypeDefinition
+unionTypeDefinition description' = Full.UnionTypeDefinition description'
+    <$ symbol "union"
+    <*> name
+    <*> directives
+    <*> option (Full.UnionMemberTypes []) (unionMemberTypes sepBy1)
+    <?> "UnionTypeDefinition"
+
+unionTypeExtension :: Parser Full.TypeExtension
+unionTypeExtension = extend "union" "UnionTypeExtension"
+    $ unionMemberTypesExtension :| [directivesExtension]
+  where
+    unionMemberTypesExtension = Full.UnionTypeUnionMemberTypesExtension
+        <$> name
+        <*> directives
+        <*> unionMemberTypes NonEmpty.sepBy1
+    directivesExtension = Full.UnionTypeDirectivesExtension
+        <$> name
+        <*> NonEmpty.some directive
+
+unionMemberTypes ::
+    Foldable t =>
+    (Parser Text -> Parser Text -> Parser (t Full.NamedType)) ->
+    Parser (Full.UnionMemberTypes t)
+unionMemberTypes sepBy' = Full.UnionMemberTypes
+    <$ equals
+    <* optional pipe
+    <*> name `sepBy'` pipe
+    <?> "UnionMemberTypes"
+
+interfaceTypeDefinition :: Full.Description -> Parser Full.TypeDefinition
+interfaceTypeDefinition description' = Full.InterfaceTypeDefinition description'
+    <$ symbol "interface"
+    <*> name
+    <*> option (Full.ImplementsInterfaces []) (implementsInterfaces sepBy1)
+    <*> directives
+    <*> braces (many fieldDefinition)
+    <?> "InterfaceTypeDefinition"
+
+interfaceTypeExtension :: Parser Full.TypeExtension
+interfaceTypeExtension = extend "interface" "InterfaceTypeExtension"
+    $ fieldsDefinitionExtension :| [directivesExtension]
+  where
+    fieldsDefinitionExtension = Full.InterfaceTypeFieldsDefinitionExtension
+        <$> name
+        <*> directives
+        <*> braces (NonEmpty.some fieldDefinition)
+    directivesExtension = Full.InterfaceTypeDirectivesExtension
+        <$> name
+        <*> NonEmpty.some directive
+
+enumTypeDefinition :: Full.Description -> Parser Full.TypeDefinition
+enumTypeDefinition description' = Full.EnumTypeDefinition description'
+    <$ symbol "enum"
+    <*> name
+    <*> directives
+    <*> listOptIn braces enumValueDefinition
+    <?> "EnumTypeDefinition"
+
+enumTypeExtension :: Parser Full.TypeExtension
+enumTypeExtension = extend "enum" "EnumTypeExtension"
+    $ enumValuesDefinitionExtension :| [directivesExtension]
+  where
+    enumValuesDefinitionExtension = Full.EnumTypeEnumValuesDefinitionExtension
+        <$> name
+        <*> directives
+        <*> braces (NonEmpty.some enumValueDefinition)
+    directivesExtension = Full.EnumTypeDirectivesExtension
+        <$> name
+        <*> NonEmpty.some directive
+
+inputObjectTypeDefinition :: Full.Description -> Parser Full.TypeDefinition
+inputObjectTypeDefinition description' = Full.InputObjectTypeDefinition description'
+    <$ symbol "input"
+    <*> name
+    <*> directives
+    <*> listOptIn braces inputValueDefinition
+    <?> "InputObjectTypeDefinition"
+
+inputObjectTypeExtension :: Parser Full.TypeExtension
+inputObjectTypeExtension = extend "input" "InputObjectTypeExtension"
+    $ inputFieldsDefinitionExtension :| [directivesExtension]
+  where
+    inputFieldsDefinitionExtension = Full.InputObjectTypeInputFieldsDefinitionExtension
+        <$> name
+        <*> directives
+        <*> braces (NonEmpty.some inputValueDefinition)
+    directivesExtension = Full.InputObjectTypeDirectivesExtension
+        <$> name
+        <*> NonEmpty.some directive
+
+enumValueDefinition :: Parser Full.EnumValueDefinition
+enumValueDefinition = Full.EnumValueDefinition
+    <$> description
+    <*> enumValue
+    <*> directives
+    <?> "EnumValueDefinition"
+
+implementsInterfaces ::
+    Foldable t =>
+    (Parser Text -> Parser Text -> Parser (t Full.NamedType)) ->
+    Parser (Full.ImplementsInterfaces t)
+implementsInterfaces sepBy' = Full.ImplementsInterfaces
+    <$ symbol "implements"
+    <* optional amp
+    <*> name `sepBy'` amp
+    <?> "ImplementsInterfaces"
+
+inputValueDefinition :: Parser Full.InputValueDefinition
+inputValueDefinition = Full.InputValueDefinition
+    <$> description
+    <*> name
+    <* colon
+    <*> type'
+    <*> defaultValue
+    <*> directives
+    <?> "InputValueDefinition"
+
+argumentsDefinition :: Parser Full.ArgumentsDefinition
+argumentsDefinition = Full.ArgumentsDefinition
+    <$> listOptIn parens inputValueDefinition
+    <?> "ArgumentsDefinition"
+
+fieldDefinition :: Parser Full.FieldDefinition
+fieldDefinition = Full.FieldDefinition
+    <$> description
+    <*> name
+    <*> argumentsDefinition
+    <* colon
+    <*> type'
+    <*> directives
+    <?> "FieldDefinition"
+
+schemaDefinition :: Parser Full.TypeSystemDefinition
+schemaDefinition = Full.SchemaDefinition
+    <$ symbol "schema"
+    <*> directives
+    <*> operationTypeDefinitions
+    <?> "SchemaDefinition"
+
+operationTypeDefinitions :: Parser (NonEmpty Full.OperationTypeDefinition)
+operationTypeDefinitions = braces $ NonEmpty.some operationTypeDefinition
+
+schemaExtension :: Parser Full.SchemaExtension
+schemaExtension = extend "schema" "SchemaExtension"
+    $ schemaOperationExtension :| [directivesExtension]
+  where
+    directivesExtension = Full.SchemaDirectivesExtension
+        <$> NonEmpty.some directive
+    schemaOperationExtension = Full.SchemaOperationExtension
+        <$> directives
+        <*> operationTypeDefinitions
+
+operationTypeDefinition :: Parser Full.OperationTypeDefinition
+operationTypeDefinition = Full.OperationTypeDefinition
+    <$> operationType <* colon
+    <*> name
+    <?> "OperationTypeDefinition"
+
+operationDefinition :: Parser Full.OperationDefinition
+operationDefinition = shorthand
+    <|> operationDefinition'
+    <?> "OperationDefinition"
+  where
+    shorthand = do
+        location <- getLocation
+        selectionSet' <- selectionSet
+        pure $ Full.SelectionSet selectionSet' location
+    operationDefinition' = do
+        location <- getLocation
+        operationType' <- operationType
+        operationName <- optional name
+        variableDefinitions' <- variableDefinitions
+        directives' <- directives
+        selectionSet' <- selectionSet
+        pure $ Full.OperationDefinition
+            operationType'
+            operationName
+            variableDefinitions'
+            directives'
+            selectionSet'
+            location
+
+operationType :: Parser Full.OperationType
+operationType = Full.Query <$ symbol "query"
+    <|> Full.Mutation <$ symbol "mutation"
+    <|> Full.Subscription <$ symbol "subscription"
+    <?> "OperationType"
+
+selectionSet :: Parser Full.SelectionSet
+selectionSet = braces (NonEmpty.some selection) <?> "SelectionSet"
+
+selectionSetOpt :: Parser Full.SelectionSetOpt
+selectionSetOpt = listOptIn braces selection <?> "SelectionSet"
+
+selection :: Parser Full.Selection
+selection = Full.FieldSelection <$> field
+    <|> Full.FragmentSpreadSelection <$> try fragmentSpread
+    <|> Full.InlineFragmentSelection <$> inlineFragment
+    <?> "Selection"
+
+field :: Parser Full.Field
+field = label "Field" $ do
+    location <- getLocation
+    alias' <- optional alias
+    name' <- name
+    arguments' <- arguments
+    directives' <- directives
+    selectionSetOpt' <- selectionSetOpt
+    pure $ Full.Field alias' name' arguments' directives' selectionSetOpt' location
+
+alias :: Parser Full.Name
+alias = try (name <* colon) <?> "Alias"
+
+arguments :: Parser [Full.Argument]
+arguments = listOptIn parens argument <?> "Arguments"
+
+argument :: Parser Full.Argument
+argument = label "Argument" $ do
+    location <- getLocation
+    name' <- name
+    colon
+    value' <- valueNode value
+    pure $ Full.Argument name' value' location
+
+fragmentSpread :: Parser Full.FragmentSpread
+fragmentSpread = label "FragmentSpread" $ do
+    location <- getLocation
+    _ <- spread
+    fragmentName' <- fragmentName
+    directives' <- directives
+    pure $ Full.FragmentSpread fragmentName' directives' location
+
+inlineFragment :: Parser Full.InlineFragment
+inlineFragment = label "InlineFragment" $ do
+    location <- getLocation
+    _ <- spread
+    typeCondition' <- optional typeCondition
+    directives' <- directives
+    selectionSet' <- selectionSet
+    pure $ Full.InlineFragment typeCondition' directives' selectionSet' location
+
+fragmentDefinition :: Parser Full.FragmentDefinition
+fragmentDefinition =  label "FragmentDefinition" $ do
+    location <- getLocation
+    _ <- symbol "fragment"
+    fragmentName' <- name
+    typeCondition' <- typeCondition
+    directives' <- directives
+    selectionSet' <- selectionSet
+    pure $ Full.FragmentDefinition
+        fragmentName' typeCondition' directives' selectionSet' location
+
+fragmentName :: Parser Full.Name
+fragmentName = but (symbol "on") *> name <?> "FragmentName"
+
+typeCondition :: Parser Full.TypeCondition
+typeCondition = symbol "on" *> name <?> "TypeCondition"
+
+valueNode :: forall a. Parser a -> Parser (Full.Node a)
+valueNode valueParser = do
+    location <- getLocation
+    value' <- valueParser
+    pure $ Full.Node value' location
+
+value :: Parser Full.Value
+value = Full.Variable <$> variable
+    <|> Full.Float <$> try float
+    <|> Full.Int <$> integer
+    <|> Full.Boolean <$> booleanValue
+    <|> Full.Null <$  nullValue
+    <|> Full.String <$> stringValue
+    <|> Full.Enum <$> try enumValue
+    <|> Full.List <$> brackets (many $ valueNode value)
+    <|> Full.Object <$> braces (many $ objectField $ valueNode value)
+    <?> "Value"
+
+constValue :: Parser Full.ConstValue
+constValue = Full.ConstFloat <$> try float
+    <|> Full.ConstInt <$> integer
+    <|> Full.ConstBoolean <$> booleanValue
+    <|> Full.ConstNull <$ nullValue
+    <|> Full.ConstString <$> stringValue
+    <|> Full.ConstEnum <$> try enumValue
+    <|> Full.ConstList <$> brackets (many $ valueNode constValue)
+    <|> Full.ConstObject <$> braces (many $ objectField $ valueNode constValue)
+    <?> "Value"
+
+booleanValue :: Parser Bool
+booleanValue = True  <$ symbol "true"
+    <|> False <$ symbol "false"
+    <?> "BooleanValue"
+
+enumValue :: Parser Full.Name
+enumValue = but (symbol "true")
+    *> but (symbol "false")
+    *> but (symbol "null")
+    *> name
+    <?> "EnumValue"
+
+stringValue :: Parser Text
+stringValue = blockString <|> string <?> "StringValue"
+
+nullValue :: Parser Text
+nullValue = symbol "null" <?> "NullValue"
+
+objectField :: forall a. Parser (Full.Node a) -> Parser (Full.ObjectField a)
+objectField valueParser = label "ObjectField" $ do
+    location <- getLocation
+    fieldName <- name
+    colon
+    fieldValue <- valueParser
+    pure $ Full.ObjectField fieldName fieldValue location
+
+variableDefinitions :: Parser [Full.VariableDefinition]
+variableDefinitions = listOptIn parens variableDefinition
+    <?> "VariableDefinitions"
+
+variableDefinition :: Parser Full.VariableDefinition
+variableDefinition = label "VariableDefinition" $ do
+    location <- getLocation
+    variableName <- variable
+    colon
+    variableType <- type'
+    variableValue <- defaultValue
+    pure $ Full.VariableDefinition variableName variableType variableValue location
+
+variable :: Parser Full.Name
+variable = dollar *> name <?> "Variable"
+
+defaultValue :: Parser (Maybe (Full.Node Full.ConstValue))
+defaultValue = optional (equals *> valueNode constValue) <?> "DefaultValue"
+
+type' :: Parser Full.Type
+type' = try (Full.TypeNonNull <$> nonNullType)
+    <|> Full.TypeList <$> brackets type'
+    <|> Full.TypeNamed <$> name
+    <?> "Type"
+
+nonNullType :: Parser Full.NonNullType
+nonNullType = Full.NonNullTypeNamed <$> name <* bang
+    <|> Full.NonNullTypeList  <$> brackets type'  <* bang
+    <?> "NonNullType"
+
+directives :: Parser [Full.Directive]
+directives = many directive <?> "Directives"
+
+directive :: Parser Full.Directive
+directive = label "Directive" $ do
+    location <- getLocation
+    at
+    directiveName <- name
+    directiveArguments <- arguments
+    pure $ Full.Directive directiveName directiveArguments location
+
+listOptIn :: (Parser [a] -> Parser [a]) -> Parser a -> Parser [a]
+listOptIn surround = option [] . surround . some
+
+-- Hack to reverse parser success
+but :: Parser a -> Parser ()
+but pn = False <$ lookAhead pn <|> pure True >>= \case
+    False -> empty
+    True  -> pure ()

src/Language/GraphQL/Error.hs

@@ -0,0 +1,93 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE ExistentialQuantification #-}
+{-# LANGUAGE RecordWildCards #-}
+
+-- | Error handling.
+module Language.GraphQL.Error
+    ( Error(..)
+    , Path(..)
+    , ResolverException(..)
+    , Response(..)
+    , ResponseEventStream
+    , parseError
+    ) where
+
+import Conduit
+import Control.Exception (Exception(..))
+import Data.Sequence (Seq(..), (|>))
+import qualified Data.Sequence as Seq
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Language.GraphQL.AST (Location(..))
+import Language.GraphQL.Execute.Coerce
+import Prelude hiding (null)
+import Text.Megaparsec
+    ( ParseErrorBundle(..)
+    , PosState(..)
+    , SourcePos(..)
+    , errorOffset
+    , parseErrorTextPretty
+    , reachOffset
+    , unPos
+    )
+
+-- | Wraps a parse error into a list of errors.
+parseError :: (Applicative f, Serialize a)
+    => ParseErrorBundle Text Void
+    -> f (Response a)
+parseError ParseErrorBundle{..}  =
+    pure $ Response null $ fst
+        $ foldl go (Seq.empty, bundlePosState) bundleErrors
+  where
+    errorObject s SourcePos{..} = Error
+        { message = Text.pack $ init $ parseErrorTextPretty s
+        , locations = [Location (unPos' sourceLine) (unPos' sourceColumn)]
+        , path = []
+        }
+    unPos' = fromIntegral . unPos
+    go (result, state) x =
+        let (_, newState) = reachOffset (errorOffset x) state
+            sourcePosition = pstateSourcePos newState
+         in (result |> errorObject x sourcePosition, newState)
+
+-- | If an error can be associated to a particular field in the GraphQL result,
+-- it must contain an entry with the key path that details the path of the
+-- response field which experienced the error. This allows clients to identify
+-- whether a null result is intentional or caused by a runtime error.
+data Path
+    = Segment Text -- ^ Field name.
+    | Index Int -- ^ List index if a field returned a list.
+    deriving (Eq, Show)
+
+-- | @GraphQL@ error.
+data Error = Error
+    { message :: Text
+    , locations :: [Location]
+    , path :: [Path]
+    } deriving (Eq, Show)
+
+-- | The server\'s response describes the result of executing the requested
+-- operation if successful, and describes any errors encountered during the
+-- request.
+data Response a = Response
+    { data' :: a
+    , errors :: Seq Error
+    } deriving (Eq, Show)
+
+-- | Each event in the underlying Source Stream triggers execution of the
+-- subscription selection set. The results of the execution generate a Response
+-- Stream.
+type ResponseEventStream m a = ConduitT () (Response a) m ()
+
+-- | Only exceptions that inherit from 'ResolverException' a cought by the
+-- executor.
+data ResolverException = forall e. Exception e => ResolverException e
+
+instance Show ResolverException where
+    show (ResolverException e) = show e
+
+instance Exception ResolverException

src/Language/GraphQL/Execute.hs

@@ -0,0 +1,725 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE ExistentialQuantification #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# LANGUAGE TypeApplications #-}
+
+-- | This module provides functions to execute a @GraphQL@ request.
+module Language.GraphQL.Execute
+    ( execute
+    , module Language.GraphQL.Execute.Coerce
+    ) where
+
+import Conduit (mapMC, (.|))
+import Control.Arrow (left)
+import Control.Monad.Catch
+     ( Exception(..)
+     , Handler(..)
+     , MonadCatch(..)
+     , MonadThrow(..)
+     , SomeException(..)
+     , catches
+     )
+import Control.Monad.Trans.Class (MonadTrans(..))
+import Control.Monad.Trans.Reader (ReaderT(..), ask, runReaderT)
+import Control.Monad.Trans.Writer (WriterT(..), runWriterT)
+import qualified Control.Monad.Trans.Writer as Writer
+import Control.Monad (foldM)
+import qualified Language.GraphQL.AST.Document as Full
+import Data.Foldable (find)
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.List.NonEmpty (NonEmpty(..))
+import qualified Data.List.NonEmpty as NonEmpty
+import Data.Maybe (fromMaybe)
+import Data.Sequence (Seq)
+import qualified Data.Sequence as Seq
+import qualified Data.Vector as Vector
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Data.Typeable (cast)
+import GHC.Records (HasField(..))
+import Language.GraphQL.Execute.Coerce
+import Language.GraphQL.Execute.OrderedMap (OrderedMap)
+import qualified Language.GraphQL.Execute.OrderedMap as OrderedMap
+import qualified Language.GraphQL.Execute.Transform as Transform
+import qualified Language.GraphQL.Type.In as In
+import qualified Language.GraphQL.Type.Out as Out
+import qualified Language.GraphQL.Type as Type
+import qualified Language.GraphQL.Type.Internal as Type.Internal
+import Language.GraphQL.Type.Schema (Schema, Type)
+import qualified Language.GraphQL.Type.Schema as Schema
+import Language.GraphQL.Error
+    ( Error(..)
+    , Response(..)
+    , Path(..)
+    , ResolverException(..)
+    , ResponseEventStream
+    )
+import Prelude hiding (null)
+import Language.GraphQL.AST.Document (showVariableName)
+
+newtype ExecutorT m a = ExecutorT
+    { runExecutorT :: ReaderT (HashMap Full.Name (Type m)) (WriterT (Seq Error) m) a
+    }
+
+instance Functor m => Functor (ExecutorT m) where
+    fmap f = ExecutorT . fmap f . runExecutorT
+
+instance Applicative m => Applicative (ExecutorT m) where
+    pure = ExecutorT . pure
+    ExecutorT f <*> ExecutorT x = ExecutorT $ f <*> x
+
+instance Monad m => Monad (ExecutorT m) where
+    ExecutorT x >>= f = ExecutorT $ x >>= runExecutorT . f
+
+instance MonadTrans ExecutorT where
+    lift = ExecutorT . lift . lift
+
+instance MonadThrow m => MonadThrow (ExecutorT m) where
+    throwM = lift . throwM
+
+instance MonadCatch m => MonadCatch (ExecutorT m) where
+  catch (ExecutorT stack) handler =
+      ExecutorT $ catch stack $ runExecutorT . handler
+
+data GraphQLException = forall e. Exception e => GraphQLException e
+
+instance Show GraphQLException where
+    show (GraphQLException e) = show e
+
+instance Exception GraphQLException
+
+graphQLExceptionToException :: Exception e => e -> SomeException
+graphQLExceptionToException = toException . GraphQLException
+
+graphQLExceptionFromException :: Exception e => SomeException -> Maybe e
+graphQLExceptionFromException e = do
+    GraphQLException graphqlException <- fromException e
+    cast graphqlException
+
+data ResultException = forall e. Exception e => ResultException e
+
+instance Show ResultException where
+    show (ResultException e) = show e
+
+instance Exception ResultException where
+    toException = graphQLExceptionToException
+    fromException = graphQLExceptionFromException
+
+resultExceptionToException :: Exception e => e -> SomeException
+resultExceptionToException = toException . ResultException
+
+resultExceptionFromException :: Exception e => SomeException -> Maybe e
+resultExceptionFromException e = do
+    ResultException resultException <- fromException e
+    cast resultException
+
+data FieldException = forall e. Exception e => FieldException Full.Location [Path] e
+
+instance Show FieldException where
+    show (FieldException _ _ e) = displayException e
+
+instance Exception FieldException where
+    toException = graphQLExceptionToException
+    fromException = graphQLExceptionFromException
+
+data ValueCompletionException = ValueCompletionException String Type.Value
+
+instance Show ValueCompletionException where
+    show (ValueCompletionException typeRepresentation found) = concat
+        [ "Value completion error. Expected type "
+        , typeRepresentation
+        , ", found: "
+        , show found
+        , "."
+        ]
+
+instance Exception ValueCompletionException where
+    toException = resultExceptionToException
+    fromException = resultExceptionFromException
+
+data InputCoercionException =
+    InputCoercionException String In.Type (Maybe (Full.Node Transform.Input))
+
+instance Show InputCoercionException where
+    show (InputCoercionException argumentName argumentType Nothing) = concat
+        [ "Required argument \""
+        , argumentName
+        , "\" of type "
+        , show argumentType
+        , " not specified."
+        ]
+    show (InputCoercionException argumentName argumentType (Just givenValue)) = concat
+        [ "Argument \""
+        , argumentName
+        , "\" has invalid type. Expected type "
+        , show argumentType
+        , ", found: "
+        , show givenValue
+        , "."
+        ]
+
+instance Exception InputCoercionException where
+    toException = graphQLExceptionToException
+    fromException = graphQLExceptionFromException
+
+newtype ResultCoercionException = ResultCoercionException String
+
+instance Show ResultCoercionException where
+    show (ResultCoercionException typeRepresentation) = concat
+        [ "Unable to coerce result to "
+        , typeRepresentation
+        , "."
+        ]
+
+instance Exception ResultCoercionException where
+    toException = resultExceptionToException
+    fromException = resultExceptionFromException
+
+-- | Query error types.
+data QueryError
+    = OperationNameRequired
+    | OperationNotFound String
+    | CoercionError Full.VariableDefinition
+    | UnknownInputType Full.VariableDefinition
+
+tell :: Monad m => Seq Error -> ExecutorT m ()
+tell = ExecutorT . lift . Writer.tell
+
+operationNameErrorText :: Text
+operationNameErrorText = Text.unlines
+    [ "Named operations must be provided with the name of the desired operation."
+    , "See https://spec.graphql.org/June2018/#sec-Language.Document description."
+    ]
+
+queryError :: QueryError -> Error
+queryError OperationNameRequired =
+    let queryErrorMessage = "Operation name is required. " <> operationNameErrorText
+    in Error{ message = queryErrorMessage, locations = [], path = [] }
+queryError (OperationNotFound operationName) =
+    let queryErrorMessage = Text.unlines
+            [ Text.concat
+              [ "Operation \""
+              , Text.pack operationName
+              , "\" is not found in the named operations you've provided. "
+              ]
+            , operationNameErrorText
+            ]
+     in Error{ message = queryErrorMessage, locations = [], path = [] }
+queryError (CoercionError variableDefinition) =
+    let (Full.VariableDefinition _ _ _ location) = variableDefinition
+        queryErrorMessage = Text.concat
+            [ "Failed to coerce the variable "
+            , Text.pack $ Full.showVariable variableDefinition
+            , "."
+            ]
+     in Error{ message = queryErrorMessage, locations = [location], path = [] }
+queryError (UnknownInputType variableDefinition) =
+    let Full.VariableDefinition _ variableTypeName _ location = variableDefinition
+        queryErrorMessage = Text.concat
+            [ "Variable "
+            , Text.pack $ showVariableName variableDefinition
+            , " has unknown type "
+            , Text.pack $ show variableTypeName
+            , "."
+            ]
+     in Error{ message = queryErrorMessage, locations = [location], path = [] }
+
+-- | The substitution is applied to the document, and the resolvers are applied
+-- to the resulting fields. The operation name can be used if the document
+-- defines multiple root operations.
+--
+-- Returns the result of the query against the schema wrapped in a /data/
+-- field, or errors wrapped in an /errors/ field.
+execute :: (MonadCatch m, VariableValue a, Serialize b)
+    => Schema m -- ^ Resolvers.
+    -> Maybe Text -- ^ Operation name.
+    -> HashMap Full.Name a -- ^ Variable substitution function.
+    -> Full.Document -- @GraphQL@ document.
+    -> m (Either (ResponseEventStream m b) (Response b))
+execute schema' operationName subs document' =
+    executeRequest schema' document' (Text.unpack <$> operationName) subs
+
+executeRequest :: (MonadCatch m, Serialize a, VariableValue b)
+    => Schema m
+    -> Full.Document
+    -> Maybe String
+    -> HashMap Full.Name b
+    -> m (Either (ResponseEventStream m a) (Response a))
+executeRequest schema sourceDocument operationName variableValues = do
+    operationAndVariables <- sequence buildOperation
+    case operationAndVariables of
+        Left queryError' -> pure
+            $ Right
+            $ Response null $ pure $ queryError queryError'
+        Right operation
+            | Transform.Operation Full.Query topSelections _operationLocation <- operation ->
+                 Right <$> executeQuery topSelections schema
+            | Transform.Operation Full.Mutation topSelections operationLocation <- operation ->
+                Right <$> executeMutation topSelections schema operationLocation
+            | Transform.Operation Full.Subscription topSelections operationLocation <- operation ->
+                either rightErrorResponse Left <$> subscribe topSelections schema operationLocation
+  where
+    schemaTypes = Schema.types schema
+    (operationDefinitions, fragmentDefinitions') =
+        Transform.document sourceDocument
+    buildOperation = do
+        operationDefinition <- getOperation operationDefinitions operationName
+        coercedVariableValues <- coerceVariableValues
+            schemaTypes
+            operationDefinition
+            variableValues
+        let replacement = Transform.Replacement
+                { variableValues = coercedVariableValues
+                , fragmentDefinitions = fragmentDefinitions'
+                , visitedFragments = mempty
+                , types = schemaTypes
+                }
+        pure $ flip runReaderT replacement
+            $ Transform.runTransformT
+            $ Transform.transform operationDefinition
+
+rightErrorResponse :: Serialize b => forall a. Error -> Either a (Response b)
+rightErrorResponse = Right . Response null . pure
+
+getOperation :: [Full.OperationDefinition] -> Maybe String -> Either QueryError Full.OperationDefinition
+getOperation [operation] Nothing = Right operation
+getOperation operations (Just givenOperationName)
+    = maybe (Left $ OperationNotFound givenOperationName) Right
+    $ find findOperationByName operations
+  where
+    findOperationByName (Full.OperationDefinition _ (Just operationName) _ _ _ _) =
+        givenOperationName == Text.unpack operationName
+    findOperationByName _ = False
+getOperation _ _ = Left OperationNameRequired
+
+executeQuery :: (MonadCatch m, Serialize a)
+    => Seq (Transform.Selection m)
+    -> Schema m
+    -> m (Response a)
+executeQuery topSelections schema = do
+    let queryType = Schema.query schema
+    (data', errors) <- runWriterT
+        $ flip runReaderT (Schema.types schema)
+        $ runExecutorT
+        $ catch (executeSelectionSet topSelections queryType Type.Null [])
+        handleException
+    pure $ Response data' errors
+
+handleException :: (MonadCatch m, Serialize a)
+    => FieldException
+    -> ExecutorT m a
+handleException (FieldException fieldLocation errorPath next) =
+    let newError = constructError next fieldLocation errorPath
+     in tell (Seq.singleton newError) >> pure null
+
+constructError :: Exception e => e -> Full.Location -> [Path] -> Error
+constructError e fieldLocation errorPath = Error
+    { message = Text.pack (displayException e)
+    , path = reverse errorPath
+    , locations = [fieldLocation]
+    }
+
+executeMutation :: (MonadCatch m, Serialize a)
+    => Seq (Transform.Selection m)
+    -> Schema m
+    -> Full.Location
+    -> m (Response a)
+executeMutation topSelections schema operationLocation
+    | Just mutationType <- Schema.mutation schema = do
+        (data', errors) <- runWriterT
+            $ flip runReaderT (Schema.types schema)
+            $ runExecutorT
+            $ catch (executeSelectionSet topSelections mutationType Type.Null [])
+            handleException
+        pure $ Response data' errors
+    | otherwise = pure
+        $ Response null
+        $ Seq.singleton
+        $ Error "Schema doesn't support mutations." [operationLocation] []
+
+executeSelectionSet :: (MonadCatch m, Serialize a)
+    => Seq (Transform.Selection m)
+    -> Out.ObjectType m
+    -> Type.Value
+    -> [Path]
+    -> ExecutorT m a
+executeSelectionSet selections objectType objectValue errorPath = do
+    let groupedFieldSet = collectFields objectType selections
+    resolvedValues <- OrderedMap.traverseMaybe go groupedFieldSet
+    coerceResult (Out.NonNullObjectType objectType) $ Object resolvedValues
+  where
+    executeField' fields resolver =
+        executeField objectValue fields resolver errorPath
+    Out.ObjectType _ _ _ resolvers = objectType
+    go fields@(Transform.Field _ fieldName _ _ _ :| _) =
+        traverse (executeField' fields) $ HashMap.lookup fieldName resolvers
+
+fieldsSegment :: forall m. NonEmpty (Transform.Field m) -> Path
+fieldsSegment (Transform.Field alias fieldName _ _ _ :| _) =
+    Segment (fromMaybe fieldName alias)
+
+viewResolver :: Out.Resolver m -> (Out.Field m, Out.Resolve m)
+viewResolver (Out.ValueResolver resolverField' resolveFunction) =
+    (resolverField', resolveFunction)
+viewResolver (Out.EventStreamResolver resolverField' resolveFunction _) =
+    (resolverField', resolveFunction)
+
+executeField :: forall m a
+    . (MonadCatch m, Serialize a)
+    => Type.Value
+    -> NonEmpty (Transform.Field m)
+    -> Out.Resolver m
+    -> [Path]
+    -> ExecutorT m a
+executeField objectValue fields (viewResolver -> resolverPair) errorPath =
+    let Transform.Field _ fieldName inputArguments _ fieldLocation :| _ = fields
+     in catches (go fieldName inputArguments)
+        [ Handler nullResultHandler
+        , Handler (inputCoercionHandler fieldLocation)
+        , Handler (resultHandler fieldLocation)
+        , Handler (resolverHandler fieldLocation)
+        ]
+  where
+    fieldErrorPath = fieldsSegment fields : errorPath
+    inputCoercionHandler :: (MonadCatch m, Serialize a)
+        => Full.Location
+        -> InputCoercionException
+        -> ExecutorT m a
+    inputCoercionHandler _ e@(InputCoercionException _ _ (Just valueNode)) =
+        let argumentLocation = getField @"location" valueNode
+         in exceptionHandler argumentLocation e
+    inputCoercionHandler fieldLocation e = exceptionHandler fieldLocation e
+    resultHandler :: (MonadCatch m, Serialize a)
+        => Full.Location
+        -> ResultException
+        -> ExecutorT m a
+    resultHandler = exceptionHandler
+    resolverHandler :: (MonadCatch m, Serialize a)
+        => Full.Location
+        -> ResolverException
+        -> ExecutorT m a
+    resolverHandler = exceptionHandler
+    nullResultHandler :: (MonadCatch m, Serialize a)
+        => FieldException
+        -> ExecutorT m a
+    nullResultHandler e@(FieldException fieldLocation errorPath' next) =
+        let newError = constructError next fieldLocation errorPath'
+         in if Out.isNonNullType fieldType
+             then throwM e
+             else returnError newError
+    exceptionHandler errorLocation e =
+        let newError = constructError e errorLocation fieldErrorPath
+         in if Out.isNonNullType fieldType
+             then throwM $ FieldException errorLocation fieldErrorPath e
+             else returnError newError
+    returnError newError = tell (Seq.singleton newError) >> pure null
+    go fieldName inputArguments = do
+        argumentValues <- coerceArgumentValues argumentTypes inputArguments
+        resolvedValue <-
+           resolveFieldValue resolveFunction objectValue fieldName argumentValues
+        completeValue fieldType fields fieldErrorPath resolvedValue
+    (resolverField, resolveFunction) = resolverPair
+    Out.Field _ fieldType argumentTypes = resolverField
+
+resolveFieldValue :: MonadCatch m
+    => Out.Resolve m
+    -> Type.Value
+    -> Full.Name
+    -> Type.Subs
+    -> ExecutorT m Type.Value
+resolveFieldValue resolver objectValue _fieldName argumentValues =
+    lift $ runReaderT resolver context
+  where
+    context = Type.Context
+        { Type.arguments = Type.Arguments argumentValues
+        , Type.values = objectValue
+        }
+
+resolveAbstractType :: Monad m
+    => Type.Internal.AbstractType m
+    -> Type.Subs
+    -> ExecutorT m (Maybe (Out.ObjectType m))
+resolveAbstractType abstractType values'
+    | Just (Type.String typeName) <- HashMap.lookup "__typename" values' = do
+        types' <- ExecutorT ask
+        case HashMap.lookup typeName types' of
+            Just (Type.Internal.ObjectType objectType) ->
+                if Type.Internal.instanceOf objectType abstractType
+                    then pure $ Just objectType
+                    else pure Nothing
+            _ -> pure Nothing
+    | otherwise = pure Nothing
+
+-- https://spec.graphql.org/October2021/#sec-Value-Completion
+completeValue :: (MonadCatch m, Serialize a)
+    => Out.Type m
+    -> NonEmpty (Transform.Field m)
+    -> [Path]
+    -> Type.Value
+    -> ExecutorT m a
+completeValue (Out.isNonNullType -> False) _ _ Type.Null =
+    pure null
+completeValue outputType@(Out.ListBaseType listType) fields errorPath (Type.List list)
+    = foldM go Vector.empty list >>= coerceResult outputType . List . Vector.toList
+  where
+    go accumulator listItem =
+        let updatedPath = Index (Vector.length accumulator) : errorPath
+         in Vector.snoc accumulator
+            <$> completeValue listType fields updatedPath listItem
+completeValue outputType@(Out.ScalarBaseType _) _ _ (Type.Int int) =
+    coerceResult outputType $ Int int
+completeValue outputType@(Out.ScalarBaseType _) _ _ (Type.Boolean boolean) =
+    coerceResult outputType $ Boolean boolean
+completeValue outputType@(Out.ScalarBaseType _) _ _ (Type.Float float) =
+    coerceResult outputType $ Float float
+completeValue outputType@(Out.ScalarBaseType _) _ _ (Type.String string) =
+    coerceResult outputType $ String string
+completeValue outputType@(Out.EnumBaseType enumType) _ _ (Type.Enum enum) =
+    let Type.EnumType _ _ enumMembers = enumType
+     in if HashMap.member enum enumMembers
+        then coerceResult outputType $ Enum enum
+        else throwM
+            $ ValueCompletionException (show outputType)
+            $ Type.Enum enum
+completeValue (Out.ObjectBaseType objectType) fields errorPath result
+    = executeSelectionSet (mergeSelectionSets fields) objectType result errorPath
+completeValue outputType@(Out.InterfaceBaseType interfaceType) fields errorPath result
+    | Type.Object objectMap <- result = do
+        let abstractType = Type.Internal.AbstractInterfaceType interfaceType
+        concreteType <- resolveAbstractType abstractType objectMap
+        case concreteType of
+            Just objectType
+                -> executeSelectionSet (mergeSelectionSets fields) objectType result
+                $ fieldsSegment fields : errorPath
+            Nothing -> throwM
+                $ ValueCompletionException (show outputType) result
+completeValue outputType@(Out.UnionBaseType unionType) fields errorPath result
+    | Type.Object objectMap <- result = do
+        let abstractType = Type.Internal.AbstractUnionType unionType
+        concreteType <- resolveAbstractType abstractType objectMap
+        case concreteType of
+            Just objectType
+                -> executeSelectionSet (mergeSelectionSets fields) objectType result
+                $ fieldsSegment fields : errorPath
+            Nothing -> throwM
+                $ ValueCompletionException (show outputType) result
+completeValue outputType _ _ result =
+    throwM $ ValueCompletionException (show outputType) result
+
+coerceResult :: (MonadCatch m, Serialize a)
+    => Out.Type m
+    -> Output a
+    -> ExecutorT m a
+coerceResult outputType result
+    | Just serialized <- serialize outputType result = pure serialized
+    | otherwise = throwM $ ResultCoercionException $ show outputType
+
+mergeSelectionSets :: MonadCatch m
+    => NonEmpty (Transform.Field m)
+    -> Seq (Transform.Selection m)
+mergeSelectionSets = foldr forEach mempty
+  where
+    forEach (Transform.Field _ _ _ fieldSelectionSet _) selectionSet' =
+        selectionSet' <> fieldSelectionSet
+
+coerceArgumentValues :: MonadCatch m
+    => HashMap Full.Name In.Argument
+    -> HashMap Full.Name (Full.Node Transform.Input)
+    -> m Type.Subs
+coerceArgumentValues argumentDefinitions argumentValues =
+    HashMap.foldrWithKey c pure argumentDefinitions mempty
+  where
+    c argumentName argumentType pure' resultMap =
+        forEach argumentName argumentType resultMap >>= pure'
+    forEach :: MonadCatch m
+         => Full.Name
+         -> In.Argument
+         -> Type.Subs
+         -> m Type.Subs
+    forEach argumentName (In.Argument _ variableType defaultValue) resultMap = do
+        let matchedMap
+                = matchFieldValues' argumentName variableType defaultValue
+                $ Just resultMap
+         in case matchedMap of
+            Just matchedValues -> pure matchedValues
+            Nothing
+                | Just inputValue <- HashMap.lookup argumentName argumentValues
+                    -> throwM
+                    $ InputCoercionException (Text.unpack argumentName) variableType
+                    $ Just inputValue
+                | otherwise -> throwM
+                    $ InputCoercionException (Text.unpack argumentName) variableType Nothing
+
+    matchFieldValues' = matchFieldValues coerceArgumentValue
+        $ Full.node <$> argumentValues
+
+    coerceArgumentValue inputType transform =
+      coerceInputLiteral inputType $ extractArgumentValue transform
+
+    extractArgumentValue (Transform.Int integer) = Type.Int integer
+    extractArgumentValue (Transform.Boolean boolean) = Type.Boolean boolean
+    extractArgumentValue (Transform.String string) = Type.String string
+    extractArgumentValue (Transform.Float float) = Type.Float float
+    extractArgumentValue (Transform.Enum enum) = Type.Enum enum
+    extractArgumentValue Transform.Null = Type.Null
+    extractArgumentValue (Transform.List list) =
+      Type.List $ extractArgumentValue <$> list
+    extractArgumentValue (Transform.Object object) =
+      Type.Object $ extractArgumentValue <$> object
+    extractArgumentValue (Transform.Variable variable) = variable
+
+collectFields :: Monad m
+    => Out.ObjectType m
+    -> Seq (Transform.Selection m)
+    -> OrderedMap (NonEmpty (Transform.Field m))
+collectFields objectType = foldl forEach OrderedMap.empty
+  where
+    forEach groupedFields (Transform.FieldSelection fieldSelection) =
+        let Transform.Field maybeAlias fieldName _ _ _ = fieldSelection
+            responseKey = fromMaybe fieldName maybeAlias
+         in OrderedMap.insert responseKey (fieldSelection :| []) groupedFields
+    forEach groupedFields (Transform.FragmentSelection selectionFragment)
+        | Transform.Fragment fragmentType fragmentSelectionSet _ <- selectionFragment
+        , Type.Internal.doesFragmentTypeApply fragmentType objectType =
+            let fragmentGroupedFieldSet =
+                    collectFields objectType fragmentSelectionSet
+             in groupedFields <> fragmentGroupedFieldSet
+        | otherwise = groupedFields
+
+coerceVariableValues :: (Monad m, VariableValue b)
+    => HashMap Full.Name (Schema.Type m)
+    -> Full.OperationDefinition
+    -> HashMap Full.Name b
+    -> Either QueryError Type.Subs
+coerceVariableValues types operationDefinition' variableValues
+    | Full.OperationDefinition _ _ variableDefinitions _ _ _ <-
+        operationDefinition'
+    = foldr forEach (Right HashMap.empty) variableDefinitions
+    | otherwise = pure mempty
+  where
+    forEach variableDefinition (Right coercedValues) =
+        let Full.VariableDefinition variableName variableTypeName defaultValue _ =
+                variableDefinition
+            defaultValue' = constValue . Full.node <$> defaultValue
+         in case Type.Internal.lookupInputType variableTypeName types of
+            Just variableType ->
+                maybe (Left $ CoercionError variableDefinition) Right
+                    $ matchFieldValues
+                        coerceVariableValue'
+                        variableValues
+                        variableName
+                        variableType
+                        defaultValue'
+                    $ Just coercedValues
+            Nothing -> Left $ UnknownInputType variableDefinition
+    forEach _ coercedValuesOrError = coercedValuesOrError
+    coerceVariableValue' variableType value'
+        = coerceVariableValue variableType value'
+        >>= coerceInputLiteral variableType
+
+constValue :: Full.ConstValue -> Type.Value
+constValue (Full.ConstInt i) = Type.Int i
+constValue (Full.ConstFloat f) = Type.Float f
+constValue (Full.ConstString x) = Type.String x
+constValue (Full.ConstBoolean b) = Type.Boolean b
+constValue Full.ConstNull = Type.Null
+constValue (Full.ConstEnum e) = Type.Enum e
+constValue (Full.ConstList list) = Type.List $ constValue . Full.node <$> list
+constValue (Full.ConstObject o) =
+    Type.Object $ HashMap.fromList $ constObjectField <$> o
+  where
+    constObjectField Full.ObjectField{value = value', ..} =
+        (name, constValue $ Full.node value')
+
+subscribe :: (MonadCatch m, Serialize a)
+    => Seq (Transform.Selection m)
+    -> Schema m
+    -> Full.Location
+    -> m (Either Error (ResponseEventStream m a))
+subscribe fields schema objectLocation
+    | Just objectType <- Schema.subscription schema = do
+        let types' = Schema.types schema
+        sourceStream <-
+            createSourceEventStream types' objectType objectLocation fields
+        let traverser =
+                mapSourceToResponseEvent types' objectType fields
+        traverse traverser sourceStream
+    | otherwise = pure $ Left
+        $ Error "Schema doesn't support subscriptions." [] []
+
+mapSourceToResponseEvent :: (MonadCatch m, Serialize a)
+    => HashMap Full.Name (Type m)
+    -> Out.ObjectType m
+    -> Seq (Transform.Selection m)
+    -> Out.SourceEventStream m
+    -> m (ResponseEventStream m a)
+mapSourceToResponseEvent types' subscriptionType fields sourceStream
+    = pure
+    $ sourceStream
+    .| mapMC (executeSubscriptionEvent types' subscriptionType fields)
+
+createSourceEventStream :: MonadCatch m
+    => HashMap Full.Name (Type m)
+    -> Out.ObjectType m
+    -> Full.Location
+    -> Seq (Transform.Selection m)
+    -> m (Either Error (Out.SourceEventStream m))
+createSourceEventStream _types subscriptionType objectLocation fields
+    | [fieldGroup] <- OrderedMap.elems groupedFieldSet
+    , Transform.Field _ fieldName arguments' _ errorLocation <-
+        NonEmpty.head fieldGroup
+    , Out.ObjectType _ _ _ fieldTypes <- subscriptionType
+    , resolverT <- fieldTypes HashMap.! fieldName
+    , Out.EventStreamResolver fieldDefinition _ resolver <- resolverT
+    , Out.Field _ _fieldType argumentDefinitions <- fieldDefinition =
+        case coerceArgumentValues argumentDefinitions arguments' of
+            Left _ -> pure
+                $ Left
+                $ Error "Argument coercion failed." [errorLocation] []
+            Right  argumentValues -> left (singleError [errorLocation])
+                <$> resolveFieldEventStream Type.Null argumentValues resolver
+    | otherwise = pure
+        $ Left
+        $ Error "Subscription contains more than one field." [objectLocation] []
+  where
+    groupedFieldSet = collectFields subscriptionType fields
+    singleError :: [Full.Location] -> String -> Error
+    singleError errorLocations message = Error (Text.pack message) errorLocations []
+
+resolveFieldEventStream :: MonadCatch m
+    => Type.Value
+    -> Type.Subs
+    -> Out.Subscribe m
+    -> m (Either String (Out.SourceEventStream m))
+resolveFieldEventStream result args resolver =
+    catch (Right <$> runReaderT resolver context) handleEventStreamError
+  where
+    handleEventStreamError :: MonadCatch m
+        => ResolverException
+        -> m (Either String (Out.SourceEventStream m))
+    handleEventStreamError = pure . Left . displayException
+    context = Type.Context
+        { Type.arguments = Type.Arguments args
+        , Type.values = result
+        }
+
+executeSubscriptionEvent :: (MonadCatch m, Serialize a)
+    => HashMap Full.Name (Type m)
+    -> Out.ObjectType m
+    -> Seq (Transform.Selection m)
+    -> Type.Value
+    -> m (Response a)
+executeSubscriptionEvent types' objectType fields initialValue = do
+    (data', errors) <- runWriterT
+        $ flip runReaderT types'
+        $ runExecutorT
+        $ catch (executeSelectionSet fields objectType initialValue [])
+        handleException
+    pure $ Response data' errors

src/Language/GraphQL/Execute/Coerce.hs

@@ -0,0 +1,224 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ViewPatterns #-}
+
+-- | Types and functions used for input and result coercion.
+module Language.GraphQL.Execute.Coerce
+    ( Output(..)
+    , Serialize(..)
+    , VariableValue(..)
+    , coerceInputLiteral
+    , matchFieldValues
+    ) where
+
+import Data.Int (Int32)
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.String (IsString(..))
+import Data.Text (Text)
+import qualified Data.Text.Lazy as Text.Lazy
+import qualified Data.Text.Lazy.Builder as Text.Builder
+import qualified Data.Text.Lazy.Builder.Int as Text.Builder
+import Language.GraphQL.AST (Name)
+import Language.GraphQL.Execute.OrderedMap (OrderedMap)
+import qualified Language.GraphQL.Execute.OrderedMap as OrderedMap
+import qualified Language.GraphQL.Type as Type
+import qualified Language.GraphQL.Type.In as In
+import qualified Language.GraphQL.Type.Out as Out
+
+-- | Since variables are passed separately from the query, in an independent
+-- format, they should be first coerced to the internal representation used by
+-- this implementation.
+class VariableValue a where
+    -- | Only a basic, format-specific, coercion must be done here. Type
+    -- correctness or nullability shouldn't be validated here, they will be
+    -- validated later. The type information is provided only as a hint.
+    --
+    -- For example @GraphQL@ prohibits the coercion from a 't:Float' to an
+    -- 't:Int', but @JSON@ doesn't have integers, so whole numbers should be
+    -- coerced to 't:Int` when receiving variables as a JSON object. The same
+    -- holds for 't:Enum'. There are formats that support enumerations, @JSON@
+    -- doesn't, so the type information is given and 'coerceVariableValue' can
+    -- check that an 't:Enum' is expected and treat the given value
+    -- appropriately. Even checking whether this value is a proper member of the
+    -- corresponding 't:Enum' type isn't required here, since this can be
+    -- checked independently.
+    --
+    -- Another example is an @ID@. @GraphQL@ explicitly allows to coerce
+    -- integers and strings to @ID@s, so if an @ID@ is received as an integer,
+    -- it can be left as is and will be coerced later.
+    --
+    -- If a value cannot be coerced without losing information, 'Nothing' should
+    -- be returned, the coercion will fail then and the query won't be executed.
+    coerceVariableValue
+        :: In.Type -- ^ Expected type (variable type given in the query).
+        -> a -- ^ Variable value being coerced.
+        -> Maybe Type.Value -- ^ Coerced value on success, 'Nothing' otherwise.
+
+instance VariableValue Type.Value where
+    coerceVariableValue _ Type.Null = Just Type.Null
+    coerceVariableValue (In.ScalarBaseType _) value = Just value
+    coerceVariableValue (In.EnumBaseType _) (Type.Enum stringValue) =
+        Just $ Type.Enum stringValue
+    coerceVariableValue (In.InputObjectBaseType objectType) value
+        | (Type.Object objectValue) <- value = do
+            let (In.InputObjectType _ _ inputFields) = objectType
+            (newObjectValue, resultMap) <- foldWithKey objectValue inputFields
+            if HashMap.null newObjectValue
+                then Just $ Type.Object resultMap
+                else Nothing
+      where
+        foldWithKey objectValue = HashMap.foldrWithKey matchFieldValues'
+            $ Just (objectValue, HashMap.empty)
+        matchFieldValues' _ _ Nothing = Nothing
+        matchFieldValues' fieldName inputField (Just (objectValue, resultMap)) =
+            let (In.InputField _ fieldType _) = inputField
+                insert = flip (HashMap.insert fieldName) resultMap
+                newObjectValue = HashMap.delete fieldName objectValue
+             in case HashMap.lookup fieldName objectValue of
+                    Just variableValue -> do
+                        coerced <- coerceVariableValue fieldType variableValue
+                        pure (newObjectValue, insert coerced)
+                    Nothing -> Just (objectValue, resultMap)
+    coerceVariableValue (In.ListBaseType listType) value
+        | (Type.List arrayValue) <- value =
+            Type.List <$> traverse (coerceVariableValue listType) arrayValue
+        | otherwise = coerceVariableValue listType value
+    coerceVariableValue _ _ = Nothing
+
+-- | Looks up a value by name in the given map, coerces it and inserts into the
+-- result map. If the coercion fails, returns 'Nothing'. If the value isn't
+-- given, but a default value is known, inserts the default value into the
+-- result map. Otherwise it fails with 'Nothing' if the Input Type is a
+-- Non-Nullable type, or returns the unchanged, original map.
+matchFieldValues :: forall a
+    . (In.Type -> a -> Maybe Type.Value)
+    -> HashMap Name a
+    -> Name
+    -> In.Type
+    -> Maybe Type.Value
+    -> Maybe (HashMap Name Type.Value)
+    -> Maybe (HashMap Name Type.Value)
+matchFieldValues coerce values' fieldName type' defaultValue resultMap =
+    case HashMap.lookup fieldName values' of
+        Just variableValue -> coerceRuntimeValue $ coerce type' variableValue
+        Nothing
+            | Just value <- defaultValue ->
+                HashMap.insert fieldName value <$> resultMap
+            | Nothing <- defaultValue
+            , In.isNonNullType type' -> Nothing
+            | otherwise -> resultMap
+  where
+    coerceRuntimeValue (Just Type.Null)
+        | In.isNonNullType type' = Nothing
+    coerceRuntimeValue coercedValue =
+        HashMap.insert fieldName <$> coercedValue <*> resultMap
+
+-- | Coerces operation arguments according to the input coercion rules for the
+-- corresponding types.
+coerceInputLiteral :: In.Type -> Type.Value -> Maybe Type.Value
+coerceInputLiteral (In.isNonNullType -> False) Type.Null = Just Type.Null
+coerceInputLiteral (In.ScalarBaseType type') value
+    | (Type.String stringValue) <- value
+    , (Type.ScalarType "String" _) <- type' = Just $ Type.String stringValue
+    | (Type.Boolean booleanValue) <- value
+    , (Type.ScalarType "Boolean" _) <- type' = Just $ Type.Boolean booleanValue
+    | (Type.Int intValue) <- value
+    , (Type.ScalarType "Int" _) <- type' = Just $ Type.Int intValue
+    | (Type.Float floatValue) <- value
+    , (Type.ScalarType "Float" _) <- type' = Just $ Type.Float floatValue
+    | (Type.Int intValue) <- value
+    , (Type.ScalarType "Float" _) <- type' =
+        Just $ Type.Float $ fromIntegral intValue
+    | (Type.String stringValue) <- value
+    , (Type.ScalarType "ID" _) <- type' = Just $ Type.String stringValue
+    | (Type.Int intValue) <- value
+    , (Type.ScalarType "ID" _) <- type' = Just $ decimal intValue
+  where
+    decimal = Type.String
+        . Text.Lazy.toStrict
+        . Text.Builder.toLazyText
+        . Text.Builder.decimal
+coerceInputLiteral (In.EnumBaseType type') (Type.Enum enumValue)
+    | member enumValue type' = Just $ Type.Enum enumValue
+  where
+    member value (Type.EnumType _ _ members) = HashMap.member value members
+coerceInputLiteral (In.InputObjectBaseType type') (Type.Object values) =
+    let (In.InputObjectType _ _ inputFields) = type'
+     in Type.Object
+            <$> HashMap.foldrWithKey (matchFieldValues' values) (Just HashMap.empty) inputFields
+  where
+    matchFieldValues' values' fieldName (In.InputField _ inputFieldType defaultValue) =
+        matchFieldValues coerceInputLiteral values' fieldName inputFieldType defaultValue
+coerceInputLiteral (In.ListBaseType listType) (Type.List list) =
+    Type.List <$> traverse (coerceInputLiteral listType) list
+coerceInputLiteral (In.ListBaseType listType) singleton =
+    wrapSingleton listType singleton
+  where
+      wrapSingleton (In.ListBaseType listType') singleton' =
+          Type.List <$> sequence [wrapSingleton listType' singleton']
+      wrapSingleton listType' singleton' =
+          Type.List <$> sequence [coerceInputLiteral listType' singleton']
+coerceInputLiteral _ _ = Nothing
+
+-- | 'Serialize' describes how a @GraphQL@ value should be serialized.
+class Serialize a where
+    -- | Serializes a @GraphQL@ value according to the given serialization
+    -- format.
+    --
+    -- Type infomration is given as a hint, e.g. if you need to know what type
+    -- is being serialized to serialize it properly. Don't do any validation for
+    -- @GraphQL@ built-in types here.
+    --
+    -- If the value cannot be serialized without losing information, return
+    -- 'Nothing' — it will cause a field error.
+    serialize :: forall m
+        . Out.Type m -- ^ Expected output type.
+        -> Output a -- ^ The value to be serialized.
+        -> Maybe a -- ^ Serialized value on success or 'Nothing'.
+    -- | __null__ representation in the given serialization format.
+    null :: a
+
+-- | Intermediate type used to serialize a @GraphQL@ value.
+--
+-- The serialization is done during the execution, and 'Output' contains
+-- already serialized data (in 'List' and 'Object') as well as the new layer
+-- that has to be serialized in the current step. So 'Output' is parameterized
+-- by the serialization format.
+data Output a
+    = Int Int32
+    | Float Double
+    | String Text
+    | Boolean Bool
+    | Enum Name
+    | List [a]
+    | Object (OrderedMap a)
+    deriving (Eq, Show)
+
+instance forall a. IsString (Output a) where
+    fromString = String . fromString
+
+instance Serialize Type.Value where
+    null = Type.Null
+    serialize (Out.ScalarBaseType scalarType) value
+        | Type.ScalarType "Int" _ <- scalarType
+        , Int int <- value = Just $ Type.Int int
+        | Type.ScalarType "Float" _ <- scalarType
+        , Float float <- value = Just $ Type.Float float
+        | Type.ScalarType "String" _ <- scalarType
+        , String string <- value = Just $ Type.String string
+        | Type.ScalarType "ID" _ <- scalarType
+        , String string <- value = Just $ Type.String string
+        | Type.ScalarType "Boolean" _ <- scalarType
+        , Boolean boolean <- value = Just $ Type.Boolean boolean
+    serialize _ (Enum enum) = Just $ Type.Enum enum
+    serialize _ (List list) = Just $ Type.List list
+    serialize _ (Object object) = Just
+        $ Type.Object
+        $ HashMap.fromList
+        $ OrderedMap.toList object
+    serialize _ _ = Nothing

src/Language/GraphQL/Execute/OrderedMap.hs

@@ -0,0 +1,148 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE ExplicitForAll #-}
+
+-- | This module contains a map data structure, that preserves insertion order.
+-- Some definitions conflict with functions from prelude, so this module should
+-- probably be imported qualified.
+module Language.GraphQL.Execute.OrderedMap
+    ( OrderedMap
+    , elems
+    , empty
+    , insert
+    , foldlWithKey'
+    , keys
+    , lookup
+    , replace
+    , singleton
+    , size
+    , toList
+    , traverseMaybe
+    ) where
+
+import qualified Data.Foldable as Foldable
+import Data.HashMap.Strict (HashMap, (!))
+import qualified Data.HashMap.Strict as HashMap
+import Data.Text (Text)
+import Data.Vector (Vector)
+import qualified Data.Vector as Vector
+import Prelude hiding (filter, lookup)
+
+-- | This map associates values with the given text keys. Insertion order is
+-- preserved. When inserting a value with a key, that is already available in
+-- the map, the existing value isn't overridden, but combined with the new value
+-- using its 'Semigroup' instance.
+--
+-- Internally this map uses an array with keys to preserve the order and an
+-- unorded map with key-value pairs.
+data OrderedMap v = OrderedMap (Vector Text) (HashMap Text v)
+    deriving (Eq)
+
+instance Functor OrderedMap where
+    fmap f (OrderedMap vector hashMap) = OrderedMap vector $ fmap f hashMap
+
+instance Foldable OrderedMap where
+    foldr f = foldrWithKey $ const f
+    null (OrderedMap vector _) = Vector.null vector
+
+instance Semigroup v => Semigroup (OrderedMap v) where
+    (<>) = foldlWithKey'
+        $ \accumulator key value -> insert key value accumulator
+
+instance Semigroup v => Monoid (OrderedMap v) where
+    mempty = empty
+
+instance Traversable OrderedMap where
+    traverse f (OrderedMap vector hashMap) = OrderedMap vector
+        <$> traverse f hashMap
+
+instance Show v => Show (OrderedMap v) where
+    showsPrec precedence map' = showParen (precedence > 10)
+        $ showString "fromList " . shows (toList map')
+
+-- * Construction
+
+-- | Constructs a map with a single element.
+singleton :: forall v. Text -> v -> OrderedMap v
+singleton key value = OrderedMap (Vector.singleton key)
+    $ HashMap.singleton key value
+
+-- | Constructs an empty map.
+empty :: forall v. OrderedMap v
+empty = OrderedMap mempty mempty
+
+-- * Traversal
+
+-- | Reduces this map by applying a binary operator from right to left to all
+-- elements, using the given starting value.
+foldrWithKey :: forall v a. (Text -> v -> a -> a) -> a -> OrderedMap v -> a
+foldrWithKey f initial (OrderedMap vector hashMap) = foldr go initial vector
+  where
+    go key = f key (hashMap ! key)
+
+-- | Reduces this map by applying a binary operator from left to right to all
+-- elements, using the given starting value.
+foldlWithKey' :: forall v a. (a -> Text -> v -> a) -> a -> OrderedMap v -> a
+foldlWithKey' f initial (OrderedMap vector hashMap) =
+    Vector.foldl' go initial vector
+  where
+    go accumulator key = f accumulator key (hashMap ! key)
+
+-- | Traverse over the elements and collect the 'Just' results.
+traverseMaybe
+    :: Applicative f
+    => forall a
+    . (a -> f (Maybe b))
+    -> OrderedMap a
+    -> f (OrderedMap b)
+traverseMaybe f orderedMap = foldlWithKey' filter empty
+    <$> traverse f orderedMap
+  where
+    filter accumulator key (Just value) = replace key value accumulator
+    filter accumulator _ Nothing = accumulator
+
+-- * Lists
+
+-- | Converts this map to the list of key-value pairs.
+toList :: forall v. OrderedMap v -> [(Text, v)]
+toList = foldrWithKey ((.) (:) . (,)) []
+
+-- | Returns a list with all keys in this map.
+keys :: forall v. OrderedMap v -> [Text]
+keys (OrderedMap vector _) = Foldable.toList vector
+
+-- | Returns a list with all elements in this map.
+elems :: forall v. OrderedMap v -> [v]
+elems = fmap snd . toList
+
+-- * Basic interface
+
+-- | Associates the specified value with the specified key in this map. If this
+-- map previously contained a mapping for the key, the existing and new values
+-- are combined.
+insert :: Semigroup v => Text -> v -> OrderedMap v -> OrderedMap v
+insert key value (OrderedMap vector hashMap)
+    | Just available <- HashMap.lookup key hashMap = OrderedMap vector
+        $ HashMap.insert key (available <> value) hashMap
+    | otherwise = OrderedMap (Vector.snoc vector key)
+        $ HashMap.insert key value hashMap
+
+-- | Associates the specified value with the specified key in this map. If this
+-- map previously contained a mapping for the key, the existing value is
+-- replaced by the new one.
+replace :: Text -> v -> OrderedMap v -> OrderedMap v
+replace key value (OrderedMap vector hashMap)
+    | HashMap.member key hashMap = OrderedMap vector
+        $ HashMap.insert key value hashMap
+    | otherwise = OrderedMap (Vector.snoc vector key)
+        $ HashMap.insert key value hashMap
+
+-- | Gives the size of this map, i.e. number of elements in it.
+size :: forall v. OrderedMap v -> Int
+size (OrderedMap vector _) = Vector.length vector
+
+-- | Looks up a value in this map by key.
+lookup :: forall v. Text -> OrderedMap v -> Maybe v
+lookup key (OrderedMap _ hashMap) = HashMap.lookup key hashMap

src/Language/GraphQL/Execute/Transform.hs

@@ -0,0 +1,325 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE NamedFieldPuns #-}
+
+-- | After the document is parsed, before getting executed, the AST is
+-- transformed into a similar, simpler AST. Performed transformations include:
+--
+--   * Replacing variables with their values.
+--   * Inlining fragments. Some fragments can be completely eliminated and
+--   replaced by the selection set they represent. Invalid (recursive and
+--   non-existing) fragments are skipped. The most fragments are inlined, so the
+--   executor doesn't have to perform additional lookups later.
+--   * Evaluating directives (@\@include@ and @\@skip@).
+--
+-- This module is also responsible for smaller rewrites that touch only parts of
+-- the original AST.
+module Language.GraphQL.Execute.Transform
+    ( Field(..)
+    , Fragment(..)
+    , Input(..)
+    , Operation(..)
+    , Replacement(..)
+    , Selection(..)
+    , TransformT(..)
+    , document
+    , transform
+    ) where
+
+import Control.Monad (foldM)
+import Control.Monad.Catch (MonadCatch(..), MonadThrow(..))
+import Control.Monad.Trans.Class (MonadTrans(..))
+import Control.Monad.Trans.Reader (ReaderT(..), local)
+import qualified Control.Monad.Trans.Reader as Reader
+import Data.Bifunctor (first)
+import Data.Functor ((<&>))
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.HashSet (HashSet)
+import qualified Data.HashSet as HashSet
+import Data.Int (Int32)
+import Data.List (intercalate)
+import qualified Data.List.NonEmpty as NonEmpty
+import Data.Maybe (fromMaybe, isJust)
+import Data.Sequence (Seq, (><))
+import qualified Data.Sequence as Seq
+import Data.Text (Text)
+import qualified Data.Text as Text
+import qualified Language.GraphQL.AST.Document as Full
+import Language.GraphQL.Type.Schema (Type)
+import qualified Language.GraphQL.Type as Type
+import qualified Language.GraphQL.Type.Definition as Definition
+import qualified Language.GraphQL.Type.Internal as Type
+import Numeric (showFloat)
+
+-- | Associates a fragment name with a list of 'Field's.
+data Replacement m = Replacement
+    { variableValues :: Type.Subs
+    , fragmentDefinitions :: HashMap Full.Name Full.FragmentDefinition
+    , visitedFragments :: HashSet Full.Name
+    , types :: HashMap Full.Name (Type m)
+    }
+
+newtype TransformT m a = TransformT
+    { runTransformT :: ReaderT (Replacement m) m a
+    }
+
+instance Functor m => Functor (TransformT m) where
+    fmap f = TransformT . fmap f . runTransformT
+
+instance Applicative m => Applicative (TransformT m) where
+    pure = TransformT . pure
+    TransformT f <*> TransformT x = TransformT $ f <*> x
+
+instance Monad m => Monad (TransformT m) where
+    TransformT x >>= f = TransformT $ x >>= runTransformT . f
+
+instance MonadTrans TransformT where
+    lift = TransformT . lift
+
+instance MonadThrow m => MonadThrow (TransformT m) where
+    throwM = lift . throwM
+
+instance MonadCatch m => MonadCatch (TransformT m) where
+  catch (TransformT stack) handler =
+      TransformT $ catch stack $ runTransformT . handler
+
+asks :: Monad m => forall a. (Replacement m -> a) -> TransformT m a
+asks = TransformT . Reader.asks
+
+-- | GraphQL has 3 operation types: queries, mutations and subscribtions.
+data Operation m
+    = Operation Full.OperationType (Seq (Selection m)) Full.Location
+
+-- | Field or inlined fragment.
+data Selection m
+    = FieldSelection (Field m)
+    | FragmentSelection (Fragment m)
+
+data Field m = Field
+    (Maybe Full.Name)
+    Full.Name
+    (HashMap Full.Name (Full.Node Input))
+    (Seq (Selection m))
+    Full.Location
+
+data Fragment m = Fragment
+    (Type.CompositeType m) (Seq (Selection m)) Full.Location
+
+data Input
+    = Variable Type.Value
+    | Int Int32
+    | Float Double
+    | String Text
+    | Boolean Bool
+    | Null
+    | Enum Full.Name
+    | List [Input]
+    | Object (HashMap Full.Name Input)
+    deriving Eq
+
+instance Show Input where
+    showList = mappend . showList'
+      where
+        showList' list = "[" ++ intercalate ", " (show <$> list) ++ "]"
+    show (Int integer) = show integer
+    show (Float float') = showFloat float' mempty
+    show (String text) = "\"" <> Text.foldr (mappend . Full.escape) "\"" text
+    show (Boolean boolean') = show boolean'
+    show Null = "null"
+    show (Enum name) = Text.unpack name
+    show (List list) = show list
+    show (Object fields) = unwords
+        [ "{"
+        , intercalate ", " (HashMap.foldrWithKey showObject [] fields)
+        , "}"
+        ]
+      where
+        showObject key value accumulator =
+            concat [Text.unpack key, ": ", show value] : accumulator
+    show variableValue = show variableValue
+
+-- | Extracts operations and fragment definitions of the document.
+document :: Full.Document
+    -> ([Full.OperationDefinition], HashMap Full.Name Full.FragmentDefinition)
+document = foldr filterOperation ([], HashMap.empty)
+  where
+    filterOperation (Full.ExecutableDefinition executableDefinition) accumulator
+        | Full.DefinitionOperation operationDefinition' <- executableDefinition =
+            first (operationDefinition' :) accumulator
+        | Full.DefinitionFragment fragmentDefinition <- executableDefinition
+        , Full.FragmentDefinition fragmentName _ _ _ _ <- fragmentDefinition =
+            HashMap.insert fragmentName fragmentDefinition <$> accumulator
+    filterOperation _ accumulator = accumulator -- Type system definitions.
+
+-- | Rewrites the original syntax tree into an intermediate representation used
+-- for the query execution.
+transform :: Monad m => Full.OperationDefinition -> TransformT m (Operation m)
+transform (Full.OperationDefinition operationType _ _ _ selectionSet' operationLocation) = do
+    transformedSelections <- selectionSet selectionSet'
+    pure $ Operation operationType transformedSelections operationLocation
+transform (Full.SelectionSet selectionSet' operationLocation) = do
+    transformedSelections <- selectionSet selectionSet'
+    pure $ Operation Full.Query transformedSelections operationLocation
+
+selectionSet :: Monad m => Full.SelectionSet -> TransformT m (Seq (Selection m))
+selectionSet = selectionSetOpt . NonEmpty.toList
+
+selectionSetOpt :: Monad m => Full.SelectionSetOpt -> TransformT m (Seq (Selection m))
+selectionSetOpt = foldM go Seq.empty
+  where
+    go accumulatedSelections currentSelection =
+        selection currentSelection <&> (accumulatedSelections ><)
+
+selection :: Monad m => Full.Selection -> TransformT m (Seq (Selection m))
+selection (Full.FieldSelection field') =
+    maybeToSelectionSet FieldSelection $ field field'
+selection (Full.FragmentSpreadSelection fragmentSpread') =
+    maybeToSelectionSet FragmentSelection $ fragmentSpread fragmentSpread'
+selection (Full.InlineFragmentSelection inlineFragment') =
+    either id (pure . FragmentSelection) <$> inlineFragment inlineFragment'
+
+maybeToSelectionSet :: Monad m
+    => forall a
+    . (a -> Selection m)
+    -> TransformT m (Maybe a)
+    -> TransformT m (Seq (Selection m))
+maybeToSelectionSet selectionType = fmap (maybe Seq.empty $ pure . selectionType)
+
+directives :: Monad m => [Full.Directive] -> TransformT m (Maybe [Definition.Directive])
+directives = fmap Type.selection . traverse directive
+
+inlineFragment :: Monad m
+    => Full.InlineFragment
+    -> TransformT m (Either (Seq (Selection m)) (Fragment m))
+inlineFragment (Full.InlineFragment maybeCondition directives' selectionSet' location)
+    | Just typeCondition <- maybeCondition = do
+        transformedSelections <- selectionSet selectionSet'
+        transformedDirectives <- directives directives'
+        maybeFragmentType <- asks
+            $ Type.lookupTypeCondition typeCondition
+            . types
+        pure $ case transformedDirectives >> maybeFragmentType of
+            Just fragmentType -> Right
+                $ Fragment fragmentType transformedSelections location
+            Nothing -> Left Seq.empty
+    | otherwise = do
+        transformedSelections <- selectionSet selectionSet'
+        transformedDirectives <- directives directives'
+        pure $ if isJust transformedDirectives
+            then Left transformedSelections
+            else Left Seq.empty
+
+fragmentSpread :: Monad m => Full.FragmentSpread -> TransformT m (Maybe (Fragment m))
+fragmentSpread (Full.FragmentSpread spreadName directives' location) = do
+    transformedDirectives <- directives directives'
+    visitedFragment <- asks $ HashSet.member spreadName . visitedFragments
+    possibleFragmentDefinition <- asks
+        $ HashMap.lookup spreadName
+        . fragmentDefinitions
+    case transformedDirectives >> possibleFragmentDefinition of
+        Just (Full.FragmentDefinition _ typeCondition _ selections _)
+            | visitedFragment -> pure Nothing
+            | otherwise -> do
+                fragmentType <- asks
+                    $ Type.lookupTypeCondition typeCondition
+                    . types
+                traverse (traverseSelections selections) fragmentType
+        Nothing -> pure Nothing
+  where
+    traverseSelections selections typeCondition = do
+        transformedSelections <- TransformT
+            $ local fragmentInserter
+            $ runTransformT
+            $ selectionSet selections
+        pure $ Fragment typeCondition transformedSelections location
+    fragmentInserter replacement@Replacement{ visitedFragments } = replacement
+        { visitedFragments = HashSet.insert spreadName visitedFragments }
+
+field :: Monad m => Full.Field -> TransformT m (Maybe (Field m))
+field (Full.Field alias' name' arguments' directives' selectionSet' location') = do
+    transformedSelections <- selectionSetOpt selectionSet'
+    transformedDirectives <- directives directives'
+    transformedArguments <- arguments arguments'
+    let transformedField = Field
+            alias'
+            name'
+            transformedArguments
+            transformedSelections
+            location'
+    pure $ transformedDirectives >> pure transformedField
+
+arguments :: Monad m => [Full.Argument] -> TransformT m (HashMap Full.Name (Full.Node Input))
+arguments = foldM go HashMap.empty
+  where
+    go accumulator (Full.Argument name' valueNode argumentLocation) = do
+        let replaceLocation = flip Full.Node argumentLocation . Full.node
+        argumentValue <- fmap replaceLocation <$> node valueNode
+        pure $ insertIfGiven name' argumentValue accumulator
+
+directive :: Monad m => Full.Directive -> TransformT m Definition.Directive
+directive (Full.Directive name' arguments' _)
+    = Definition.Directive name'
+    . Type.Arguments
+    <$> foldM go HashMap.empty arguments'
+  where
+    go accumulator (Full.Argument argumentName Full.Node{ node = node' } _) = do
+        transformedValue <- directiveValue node'
+        pure $ HashMap.insert argumentName transformedValue accumulator
+
+directiveValue :: Monad m => Full.Value -> TransformT m Type.Value
+directiveValue = \case
+    (Full.Variable name') -> asks
+        $ HashMap.lookupDefault Type.Null name'
+        . variableValues
+    (Full.Int integer) -> pure $ Type.Int integer
+    (Full.Float double) -> pure $ Type.Float double
+    (Full.String string) -> pure $ Type.String string
+    (Full.Boolean boolean) -> pure $ Type.Boolean boolean
+    Full.Null -> pure Type.Null
+    (Full.Enum enum) -> pure $ Type.Enum enum
+    (Full.List list) -> Type.List <$> traverse directiveNode list
+    (Full.Object objectFields) ->
+        Type.Object <$> foldM objectField HashMap.empty objectFields
+  where
+    directiveNode Full.Node{ node = node'} = directiveValue node'
+    objectField accumulator Full.ObjectField{ name, value } = do
+        transformedValue <- directiveNode value
+        pure $ HashMap.insert name transformedValue accumulator
+
+input :: Monad m => Full.Value -> TransformT m (Maybe Input)
+input (Full.Variable name') =
+    asks (HashMap.lookup name' . variableValues) <&> fmap Variable
+input (Full.Int integer) = pure $ Just $ Int integer
+input (Full.Float double) = pure $ Just $ Float double
+input (Full.String string) = pure $ Just $ String string
+input (Full.Boolean boolean) = pure $ Just $ Boolean boolean
+input Full.Null = pure $ Just Null
+input (Full.Enum enum) = pure $ Just $ Enum enum
+input (Full.List list) = Just . List
+    <$> traverse (fmap (fromMaybe Null) . input . Full.node) list
+input (Full.Object objectFields) = Just . Object
+    <$> foldM objectField HashMap.empty objectFields
+  where
+    objectField accumulator Full.ObjectField{..} = do
+        objectFieldValue <- fmap Full.node <$> node value
+        pure $ insertIfGiven name objectFieldValue accumulator
+
+insertIfGiven :: forall a
+    . Full.Name
+    -> Maybe a
+    -> HashMap Full.Name a
+    -> HashMap Full.Name a
+insertIfGiven name (Just v) = HashMap.insert name v
+insertIfGiven _ _ = id
+
+node :: Monad m => Full.Node Full.Value -> TransformT m (Maybe (Full.Node Input))
+node Full.Node{node = node', ..} =
+    traverse Full.Node <$> input node' <*> pure location
+

src/Language/GraphQL/Type.hs

@@ -0,0 +1,26 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+-- | Reexports non-conflicting type system and schema definitions.
+module Language.GraphQL.Type
+    ( In.InputField(..)
+    , In.InputObjectType(..)
+    , Out.Context(..)
+    , Out.Field(..)
+    , Out.InterfaceType(..)
+    , Out.ObjectType(..)
+    , Out.Resolve
+    , Out.Resolver(..)
+    , Out.SourceEventStream
+    , Out.Subscribe
+    , Out.UnionType(..)
+    , Out.argument
+    , module Language.GraphQL.Type.Definition
+    , module Language.GraphQL.Type.Schema
+    ) where
+
+import Language.GraphQL.Type.Definition
+import Language.GraphQL.Type.Schema (Schema, schema, schemaWithTypes)
+import qualified Language.GraphQL.Type.In as In
+import qualified Language.GraphQL.Type.Out as Out

src/Language/GraphQL/Type/Definition.hs

@@ -0,0 +1,219 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE Safe #-}
+
+-- | Types that can be used as both input and output types.
+module Language.GraphQL.Type.Definition
+    ( Arguments(..)
+    , Directive(..)
+    , EnumType(..)
+    , EnumValue(..)
+    , ScalarType(..)
+    , Subs
+    , Value(..)
+    , boolean
+    , float
+    , id
+    , int
+    , showNonNullType
+    , showNonNullListType
+    , selection
+    , string
+    ) where
+
+import Data.Int (Int32)
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.List (intercalate)
+import Data.String (IsString(..))
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Language.GraphQL.AST (Name, escape)
+import Numeric (showFloat)
+import Prelude hiding (id)
+
+-- | Represents accordingly typed GraphQL values.
+data Value
+    = Int Int32
+    | Float Double -- ^ GraphQL Float is double precision.
+    | String Text
+    | Boolean Bool
+    | Null
+    | Enum Name
+    | List [Value] -- ^ Arbitrary nested list.
+    | Object (HashMap Name Value)
+    deriving Eq
+
+instance Show Value where
+    showList = mappend . showList'
+      where
+        showList' list = "[" ++ intercalate ", " (show <$> list) ++ "]"
+    show (Int integer) = show integer
+    show (Float float') = showFloat float' mempty
+    show (String text) = "\"" <> Text.foldr (mappend . escape) "\"" text
+    show (Boolean boolean') = show boolean'
+    show Null = "null"
+    show (Enum name) = Text.unpack name
+    show (List list) = show list
+    show (Object fields) = unwords
+        [ "{"
+        , intercalate ", " (HashMap.foldrWithKey showObject [] fields)
+        , "}"
+        ]
+      where
+        showObject key value accumulator =
+            concat [Text.unpack key, ": ", show value] : accumulator
+
+instance IsString Value where
+    fromString = String . fromString
+
+-- | Contains variables for the query. The key of the map is a variable name,
+-- and the value is the variable value.
+type Subs = HashMap Name Value
+
+-- | Argument list.
+newtype Arguments = Arguments (HashMap Name Value)
+    deriving (Eq, Show)
+
+instance Semigroup Arguments where
+    (Arguments x) <> (Arguments y) = Arguments $ x <> y
+
+instance Monoid Arguments where
+    mempty = Arguments mempty
+
+-- | Scalar type definition.
+--
+-- The leaf values of any request and input values to arguments are Scalars (or
+-- Enums) .
+data ScalarType = ScalarType Name (Maybe Text)
+
+instance Eq ScalarType where
+    (ScalarType this _) == (ScalarType that _) = this == that
+
+instance Show ScalarType where
+    show (ScalarType typeName _) = Text.unpack typeName
+
+-- | Enum type definition.
+--
+-- Some leaf values of requests and input values are Enums. GraphQL serializes
+-- Enum values as strings, however internally Enums can be represented by any
+-- kind of type, often integers.
+data EnumType = EnumType Name (Maybe Text) (HashMap Name EnumValue)
+
+instance Eq EnumType where
+    (EnumType this _ _) == (EnumType that _ _) = this == that
+
+instance Show EnumType where
+    show (EnumType typeName _ _) = Text.unpack typeName
+
+-- | Enum value is a single member of an 'EnumType'.
+newtype EnumValue = EnumValue (Maybe Text)
+
+-- | The @String@ scalar type represents textual data, represented as UTF-8
+-- character sequences. The String type is most often used by GraphQL to
+-- represent free-form human-readable text.
+string :: ScalarType
+string = ScalarType "String" (Just description)
+  where
+    description =
+        "The `String` scalar type represents textual data, represented as \
+        \UTF-8 character sequences. The String type is most often used by \
+        \GraphQL to represent free-form human-readable text."
+
+-- | The @Boolean@ scalar type represents @true@ or @false@.
+boolean :: ScalarType
+boolean = ScalarType "Boolean" (Just description)
+  where
+    description = "The `Boolean` scalar type represents `true` or `false`."
+
+-- | The @Int@ scalar type represents non-fractional signed whole numeric
+-- values. Int can represent values between \(-2^{31}\) and \(2^{31 - 1}\).
+int :: ScalarType
+int = ScalarType "Int" (Just description)
+  where
+    description =
+        "The `Int` scalar type represents non-fractional signed whole numeric \
+        \values. Int can represent values between -(2^31) and 2^31 - 1."
+
+-- | The @Float@ scalar type represents signed double-precision fractional
+-- values as specified by
+-- [IEEE 754](https://en.wikipedia.org/wiki/IEEE_floating_point).
+float :: ScalarType
+float = ScalarType "Float" (Just description)
+  where
+    description =
+        "The `Float` scalar type represents signed double-precision fractional \
+        \values as specified by \
+        \[IEEE 754](https://en.wikipedia.org/wiki/IEEE_floating_point)."
+
+-- | The @ID@ scalar type represents a unique identifier, often used to refetch
+-- an object or as key for a cache. The ID type appears in a JSON response as a
+-- String; however, it is not intended to be human-readable. When expected as an
+-- input type, any string (such as @"4"@) or integer (such as @4@) input value
+-- will be accepted as an ID.
+id :: ScalarType
+id = ScalarType "ID" (Just description)
+  where
+    description =
+        "The `ID` scalar type represents a unique identifier, often used to \
+        \refetch an object or as key for a cache. The ID type appears in a \
+        \JSON response as a String; however, it is not intended to be \
+        \human-readable. When expected as an input type, any string (such as \
+        \`\"4\"`) or integer (such as `4`) input value will be accepted as an ID."
+
+-- | Directive.
+data Directive = Directive Name Arguments
+    deriving (Eq, Show)
+
+-- | Directive processing status.
+data Status
+    = Skip -- ^ Skip the selection and stop directive processing
+    | Include Directive -- ^ The directive was processed, try other handlers
+    | Continue Directive -- ^ Directive handler mismatch, try other handlers
+
+-- | Takes a list of directives, handles supported directives and excludes them
+--   from the result. If the selection should be skipped, returns 'Nothing'.
+selection :: [Directive] -> Maybe [Directive]
+selection = foldr go (Just [])
+  where
+    go directive' directives' =
+        case (skip . include) (Continue directive') of
+            (Include _) -> directives'
+            Skip -> Nothing
+            (Continue x) -> (x :) <$> directives'
+
+handle :: (Directive -> Status) -> Status -> Status
+handle _ Skip = Skip
+handle handler (Continue directive) = handler directive
+handle handler (Include directive) = handler directive
+
+-- * Directive implementations
+
+skip :: Status -> Status
+skip = handle skip'
+  where
+    skip' directive'@(Directive "skip" (Arguments arguments)) =
+        case HashMap.lookup "if" arguments of
+            (Just (Boolean True)) -> Skip
+            _ -> Include directive'
+    skip' directive' = Continue directive'
+
+include :: Status -> Status
+include = handle include'
+  where
+    include' directive'@(Directive "include" (Arguments arguments)) =
+        case HashMap.lookup "if" arguments of
+            (Just (Boolean True)) -> Include directive'
+            _ -> Skip
+    include' directive' = Continue directive'
+
+showNonNullType :: Show a => a -> String
+showNonNullType = (++ "!") . show
+
+showNonNullListType :: Show a => a -> String
+showNonNullListType listType =
+    let representation = show listType
+     in concat ["[", representation, "]!"]

src/Language/GraphQL/Type/In.hs

@@ -0,0 +1,126 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE Safe #-}
+{-# LANGUAGE ViewPatterns #-}
+
+-- | Input types and values.
+--
+-- This module is intended to be imported qualified, to avoid name clashes
+-- with 'Language.GraphQL.Type.Out'.
+module Language.GraphQL.Type.In
+    ( Argument(..)
+    , Arguments
+    , InputField(..)
+    , InputObjectType(..)
+    , Type(..)
+    , isNonNullType
+    , pattern EnumBaseType
+    , pattern ListBaseType
+    , pattern InputObjectBaseType
+    , pattern ScalarBaseType
+    ) where
+
+import Data.HashMap.Strict (HashMap)
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Language.GraphQL.AST.Document (Name)
+import qualified Language.GraphQL.Type.Definition as Definition
+
+-- | Single field of an 'InputObjectType'.
+data InputField = InputField (Maybe Text) Type (Maybe Definition.Value)
+
+-- | Input object type definition.
+--
+-- An input object defines a structured collection of fields which may be
+-- supplied to a field argument.
+data InputObjectType = InputObjectType
+    Name (Maybe Text) (HashMap Name InputField)
+
+instance Eq InputObjectType where
+    (InputObjectType this _ _) == (InputObjectType that _ _) = this == that
+
+instance Show InputObjectType where
+    show (InputObjectType typeName _ _) = Text.unpack typeName
+
+-- | These types may be used as input types for arguments and directives.
+--
+-- GraphQL distinguishes between "wrapping" and "named" types. Each wrapping
+-- type can wrap other wrapping or named types. Wrapping types are lists and
+-- Non-Null types (named types are nullable by default).
+data Type
+    = NamedScalarType Definition.ScalarType
+    | NamedEnumType Definition.EnumType
+    | NamedInputObjectType InputObjectType
+    | ListType Type
+    | NonNullScalarType Definition.ScalarType
+    | NonNullEnumType Definition.EnumType
+    | NonNullInputObjectType InputObjectType
+    | NonNullListType Type
+    deriving Eq
+
+instance Show Type where
+    show (NamedScalarType scalarType) = show scalarType
+    show (NamedEnumType enumType) = show enumType
+    show (NamedInputObjectType inputObjectType) = show inputObjectType
+    show (ListType baseType) = concat ["[", show baseType, "]"]
+    show (NonNullScalarType scalarType) = Definition.showNonNullType scalarType
+    show (NonNullEnumType enumType) = Definition.showNonNullType enumType
+    show (NonNullInputObjectType inputObjectType) =
+        Definition.showNonNullType inputObjectType
+    show (NonNullListType baseType) = Definition.showNonNullListType baseType
+
+-- | Field argument definition.
+data Argument = Argument (Maybe Text) Type (Maybe Definition.Value)
+    deriving Eq
+
+-- | Field argument definitions.
+type Arguments = HashMap Name Argument
+
+-- | Matches either 'NamedScalarType' or 'NonNullScalarType'.
+pattern ScalarBaseType :: Definition.ScalarType -> Type
+pattern ScalarBaseType scalarType <- (isScalarType -> Just scalarType)
+
+-- | Matches either 'NamedEnumType' or 'NonNullEnumType'.
+pattern EnumBaseType :: Definition.EnumType -> Type
+pattern EnumBaseType enumType <- (isEnumType -> Just enumType)
+
+-- | Matches either 'NamedInputObjectType' or 'NonNullInputObjectType'.
+pattern InputObjectBaseType :: InputObjectType -> Type
+pattern InputObjectBaseType objectType <- (isInputObjectType -> Just objectType)
+
+-- | Matches either 'ListType' or 'NonNullListType'.
+pattern ListBaseType :: Type -> Type
+pattern ListBaseType listType <- (isListType -> Just listType)
+
+{-# COMPLETE EnumBaseType, ListBaseType, InputObjectBaseType, ScalarBaseType #-}
+
+isScalarType :: Type -> Maybe Definition.ScalarType
+isScalarType (NamedScalarType inputType) = Just inputType
+isScalarType (NonNullScalarType inputType) = Just inputType
+isScalarType _ = Nothing
+
+isInputObjectType :: Type -> Maybe InputObjectType
+isInputObjectType (NamedInputObjectType inputType) = Just inputType
+isInputObjectType (NonNullInputObjectType inputType) = Just inputType
+isInputObjectType _ = Nothing
+
+isEnumType :: Type -> Maybe Definition.EnumType
+isEnumType (NamedEnumType inputType) = Just inputType
+isEnumType (NonNullEnumType inputType) = Just inputType
+isEnumType _ = Nothing
+
+isListType :: Type -> Maybe Type
+isListType (ListType inputType) = Just inputType
+isListType (NonNullListType inputType) = Just inputType
+isListType _ = Nothing
+
+-- | Checks whether the given input type is a non-null type.
+isNonNullType :: Type -> Bool
+isNonNullType (NonNullScalarType _) = True
+isNonNullType (NonNullEnumType _) = True
+isNonNullType (NonNullInputObjectType _) = True
+isNonNullType (NonNullListType _) = True
+isNonNullType _ = False

src/Language/GraphQL/Type/Internal.hs

@@ -0,0 +1,204 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE LambdaCase #-}
+
+module Language.GraphQL.Type.Internal
+    ( AbstractType(..)
+    , CompositeType(..)
+    , Directive(..)
+    , Directives
+    , Schema(..)
+    , Type(..)
+    , description
+    , directives
+    , doesFragmentTypeApply
+    , implementations
+    , instanceOf
+    , lookupCompositeField
+    , lookupInputType
+    , lookupTypeCondition
+    , lookupTypeField
+    , mutation
+    , outToComposite
+    , subscription
+    , query
+    , types
+    ) where
+
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.Text (Text)
+import qualified Language.GraphQL.AST as Full
+import Language.GraphQL.AST.DirectiveLocation (DirectiveLocation)
+import qualified Language.GraphQL.Type.Definition as Definition
+import qualified Language.GraphQL.Type.In as In
+import qualified Language.GraphQL.Type.Out as Out
+
+-- | These are all of the possible kinds of types.
+data Type m
+    = ScalarType Definition.ScalarType
+    | EnumType Definition.EnumType
+    | ObjectType (Out.ObjectType m)
+    | InputObjectType In.InputObjectType
+    | InterfaceType (Out.InterfaceType m)
+    | UnionType (Out.UnionType m)
+    deriving Eq
+
+-- | Directive definition.
+--
+-- A definition consists of an optional description, arguments, whether the
+-- directive is repeatable, and the allowed directive locations.
+data Directive = Directive (Maybe Text) In.Arguments Bool [DirectiveLocation]
+    deriving Eq
+
+-- | Directive definitions.
+type Directives = HashMap Full.Name Directive
+
+-- | A Schema is created by supplying the root types of each type of operation,
+--   query and mutation (optional). A schema definition is then supplied to the
+--   validator and executor.
+data Schema m = Schema
+    (Maybe Text) -- ^ Description.
+    (Out.ObjectType m) -- ^ Query.
+    (Maybe (Out.ObjectType m)) -- ^ Mutation.
+    (Maybe (Out.ObjectType m)) -- ^ Subscription.
+    Directives -- ^ Directives
+    (HashMap Full.Name (Type m)) -- ^ Types.
+    -- Interface implementations (used only for faster access).
+    (HashMap Full.Name [Type m])
+
+-- | Schema description.
+description :: forall m. Schema m -> Maybe Text
+description (Schema description' _ _ _ _ _ _) = description'
+
+-- | Schema query type.
+query :: forall m. Schema m -> Out.ObjectType m
+query (Schema _ query' _ _ _ _ _) = query'
+
+-- | Schema mutation type.
+mutation :: forall m. Schema m -> Maybe (Out.ObjectType m)
+mutation (Schema _ _ mutation' _ _ _ _) = mutation'
+
+-- | Schema subscription type.
+subscription :: forall m. Schema m -> Maybe (Out.ObjectType m)
+subscription (Schema _ _ _ subscription' _ _ _) = subscription'
+
+-- | Schema directive definitions.
+directives :: forall m. Schema m -> Directives
+directives (Schema _ _ _ _ directives' _ _) = directives'
+
+-- | Types referenced by the schema.
+types :: forall m. Schema m -> HashMap Full.Name (Type m)
+types (Schema _ _ _ _ _ types' _) = types'
+
+-- | Interface implementations.
+implementations :: forall m. Schema m -> HashMap Full.Name [Type m]
+implementations (Schema _ _ _ _ _ _ implementations') = implementations'
+
+-- | These types may describe the parent context of a selection set.
+data CompositeType m
+    = CompositeUnionType (Out.UnionType m)
+    | CompositeObjectType (Out.ObjectType m)
+    | CompositeInterfaceType (Out.InterfaceType m)
+    deriving Eq
+
+-- | These types may describe the parent context of a selection set.
+data AbstractType m
+    = AbstractUnionType (Out.UnionType m)
+    | AbstractInterfaceType (Out.InterfaceType m)
+    deriving Eq
+
+doesFragmentTypeApply :: forall m
+    . CompositeType m
+    -> Out.ObjectType m
+    -> Bool
+doesFragmentTypeApply (CompositeObjectType fragmentType) objectType =
+    fragmentType == objectType
+doesFragmentTypeApply (CompositeInterfaceType fragmentType) objectType =
+    instanceOf objectType $ AbstractInterfaceType fragmentType
+doesFragmentTypeApply (CompositeUnionType fragmentType) objectType =
+    instanceOf objectType $ AbstractUnionType fragmentType
+
+instanceOf :: forall m. Out.ObjectType m -> AbstractType m -> Bool
+instanceOf objectType (AbstractInterfaceType interfaceType) =
+    let Out.ObjectType _ _ interfaces _ = objectType
+     in foldr go False interfaces
+  where
+    go objectInterfaceType@(Out.InterfaceType _ _ interfaces _) acc =
+        acc || foldr go (interfaceType == objectInterfaceType) interfaces
+instanceOf objectType (AbstractUnionType unionType) =
+    let Out.UnionType _ _ members = unionType
+     in foldr go False members
+  where
+    go unionMemberType acc = acc || objectType == unionMemberType
+
+lookupTypeCondition :: forall m
+    . Full.Name
+    -> HashMap Full.Name (Type m)
+    -> Maybe (CompositeType m)
+lookupTypeCondition type' types' =
+    case HashMap.lookup type' types' of
+        Just (ObjectType objectType) ->
+            Just $ CompositeObjectType objectType
+        Just (UnionType unionType) -> Just $ CompositeUnionType unionType
+        Just (InterfaceType interfaceType) ->
+            Just $ CompositeInterfaceType interfaceType
+        _ -> Nothing
+
+lookupInputType :: Full.Type -> HashMap Full.Name (Type m) -> Maybe In.Type
+lookupInputType (Full.TypeNamed name) types' =
+    case HashMap.lookup name types' of
+        Just (ScalarType scalarType) ->
+            Just $ In.NamedScalarType scalarType
+        Just (EnumType enumType) ->
+            Just $ In.NamedEnumType enumType
+        Just (InputObjectType objectType) ->
+            Just $ In.NamedInputObjectType objectType
+        _ -> Nothing
+lookupInputType (Full.TypeList list) types'
+    = In.ListType
+    <$> lookupInputType list types'
+lookupInputType (Full.TypeNonNull (Full.NonNullTypeNamed nonNull)) types' =
+    case HashMap.lookup nonNull types' of
+        Just (ScalarType scalarType) ->
+            Just $ In.NonNullScalarType scalarType
+        Just (EnumType enumType) ->
+            Just $ In.NonNullEnumType enumType
+        Just (InputObjectType objectType) ->
+            Just $ In.NonNullInputObjectType objectType
+        _ -> Nothing
+lookupInputType (Full.TypeNonNull (Full.NonNullTypeList nonNull)) types'
+    = In.NonNullListType
+    <$> lookupInputType nonNull types'
+
+lookupTypeField :: forall a. Full.Name -> Out.Type a -> Maybe (Out.Field a)
+lookupTypeField fieldName outputType =
+    outToComposite outputType >>= lookupCompositeField fieldName
+
+lookupCompositeField :: forall a
+    . Full.Name
+    -> CompositeType a
+    -> Maybe (Out.Field a)
+lookupCompositeField fieldName = \case
+    CompositeObjectType objectType -> objectChild objectType
+    CompositeInterfaceType interfaceType -> interfaceChild interfaceType
+    _ -> Nothing
+  where
+    objectChild (Out.ObjectType _ _ _ resolvers) =
+        resolverType <$> HashMap.lookup fieldName resolvers
+    interfaceChild (Out.InterfaceType _ _ _ fields) =
+        HashMap.lookup fieldName fields
+    resolverType (Out.ValueResolver objectField _) = objectField
+    resolverType (Out.EventStreamResolver objectField _ _) = objectField
+
+outToComposite :: forall a. Out.Type a -> Maybe (CompositeType a)
+outToComposite = \case
+    Out.ObjectBaseType objectType -> Just $ CompositeObjectType objectType
+    Out.InterfaceBaseType interfaceType ->
+        Just $ CompositeInterfaceType interfaceType
+    Out.UnionBaseType unionType -> Just $ CompositeUnionType unionType
+    Out.ListBaseType listType -> outToComposite listType
+    _ -> Nothing

src/Language/GraphQL/Type/Out.hs

@@ -0,0 +1,236 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE ViewPatterns #-}
+
+-- | Output types and values, monad transformer stack used by the @GraphQL@
+-- resolvers.
+--
+-- This module is intended to be imported qualified, to avoid name clashes
+-- with 'Language.GraphQL.Type.In'.
+module Language.GraphQL.Type.Out
+    ( Context(..)
+    , Field(..)
+    , InterfaceType(..)
+    , ObjectType(..)
+    , Resolve
+    , Subscribe
+    , Resolver(..)
+    , SourceEventStream
+    , Type(..)
+    , UnionType(..)
+    , argument
+    , isNonNullType
+    , pattern EnumBaseType
+    , pattern InterfaceBaseType
+    , pattern ListBaseType
+    , pattern ObjectBaseType
+    , pattern ScalarBaseType
+    , pattern UnionBaseType
+    ) where
+
+import Conduit
+import Control.Monad.Trans.Reader (ReaderT, asks)
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.Maybe (fromMaybe)
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Language.GraphQL.AST (Name)
+import Language.GraphQL.Type.Definition
+import qualified Language.GraphQL.Type.In as In
+
+-- | Object type definition.
+--
+-- Almost all of the GraphQL types you define will be object types. Object
+-- types have a name, but most importantly describe their fields.
+data ObjectType m = ObjectType
+    Name (Maybe Text) [InterfaceType m] (HashMap Name (Resolver m))
+
+instance forall a. Eq (ObjectType a) where
+    (ObjectType this _ _ _) == (ObjectType that _ _ _) = this == that
+
+instance forall a. Show (ObjectType a) where
+    show (ObjectType typeName _ _ _) = Text.unpack typeName
+
+-- | Interface Type Definition.
+--
+-- When a field can return one of a heterogeneous set of types, a Interface type
+-- is used to describe what types are possible, and what fields are in common
+-- across all types.
+data InterfaceType m = InterfaceType
+    Name (Maybe Text) [InterfaceType m] (HashMap Name (Field m))
+
+instance forall a. Eq (InterfaceType a) where
+    (InterfaceType this _ _ _) == (InterfaceType that _ _ _) = this == that
+
+instance forall a. Show (InterfaceType a) where
+    show (InterfaceType typeName _ _ _) = Text.unpack typeName
+
+-- | Union Type Definition.
+--
+-- When a field can return one of a heterogeneous set of types, a Union type is
+-- used to describe what types are possible.
+data UnionType m = UnionType Name (Maybe Text) [ObjectType m]
+
+instance forall a. Eq (UnionType a) where
+    (UnionType this _ _) == (UnionType that _ _) = this == that
+
+instance forall a. Show (UnionType a) where
+    show (UnionType typeName _ _) = Text.unpack typeName
+
+-- | Output object field definition.
+data Field m = Field
+    (Maybe Text) -- ^ Description.
+    (Type m) -- ^ Field type.
+    In.Arguments -- ^ Arguments.
+
+-- | These types may be used as output types as the result of fields.
+--
+-- GraphQL distinguishes between "wrapping" and "named" types. Each wrapping
+-- type can wrap other wrapping or named types. Wrapping types are lists and
+-- Non-Null types (named types are nullable by default).
+data Type m
+    = NamedScalarType ScalarType
+    | NamedEnumType EnumType
+    | NamedObjectType (ObjectType m)
+    | NamedInterfaceType (InterfaceType m)
+    | NamedUnionType (UnionType m)
+    | ListType (Type m)
+    | NonNullScalarType ScalarType
+    | NonNullEnumType EnumType
+    | NonNullObjectType (ObjectType m)
+    | NonNullInterfaceType (InterfaceType m)
+    | NonNullUnionType (UnionType m)
+    | NonNullListType (Type m)
+    deriving Eq
+
+instance forall a. Show (Type a) where
+    show (NamedScalarType scalarType) = show scalarType
+    show (NamedEnumType enumType) = show enumType
+    show (NamedObjectType inputObjectType) = show inputObjectType
+    show (NamedInterfaceType interfaceType) = show interfaceType
+    show (NamedUnionType unionType) = show unionType
+    show (ListType baseType) = concat ["[", show baseType, "]"]
+    show (NonNullScalarType scalarType) = showNonNullType scalarType
+    show (NonNullEnumType enumType) = showNonNullType enumType
+    show (NonNullObjectType inputObjectType) = showNonNullType inputObjectType
+    show (NonNullInterfaceType interfaceType) = showNonNullType interfaceType
+    show (NonNullUnionType unionType) = showNonNullType unionType
+    show (NonNullListType baseType) = showNonNullListType baseType
+
+-- | Matches either 'NamedScalarType' or 'NonNullScalarType'.
+pattern ScalarBaseType :: forall m. ScalarType -> Type m
+pattern ScalarBaseType scalarType <- (isScalarType -> Just scalarType)
+
+-- | Matches either 'NamedEnumType' or 'NonNullEnumType'.
+pattern EnumBaseType :: forall m. EnumType -> Type m
+pattern EnumBaseType enumType <- (isEnumType -> Just enumType)
+
+-- | Matches either 'NamedObjectType' or 'NonNullObjectType'.
+pattern ObjectBaseType :: forall m. ObjectType m -> Type m
+pattern ObjectBaseType objectType <- (isObjectType -> Just objectType)
+
+-- | Matches either 'NamedInterfaceType' or 'NonNullInterfaceType'.
+pattern InterfaceBaseType :: forall m. InterfaceType m -> Type m
+pattern InterfaceBaseType interfaceType <-
+    (isInterfaceType -> Just interfaceType)
+
+-- | Matches either 'NamedUnionType' or 'NonNullUnionType'.
+pattern UnionBaseType :: forall m. UnionType m -> Type m
+pattern UnionBaseType unionType <- (isUnionType -> Just unionType)
+
+-- | Matches either 'ListType' or 'NonNullListType'.
+pattern ListBaseType :: forall m. Type m -> Type m
+pattern ListBaseType listType <- (isListType -> Just listType)
+
+{-# COMPLETE ScalarBaseType
+    , EnumBaseType
+    , ObjectBaseType
+    , ListBaseType
+    , InterfaceBaseType
+    , UnionBaseType
+    #-}
+
+isScalarType :: forall m. Type m -> Maybe ScalarType
+isScalarType (NamedScalarType outputType) = Just outputType
+isScalarType (NonNullScalarType outputType) = Just outputType
+isScalarType _ = Nothing
+
+isObjectType :: forall m. Type m -> Maybe (ObjectType m)
+isObjectType (NamedObjectType outputType) = Just outputType
+isObjectType (NonNullObjectType outputType) = Just outputType
+isObjectType _ = Nothing
+
+isEnumType :: forall m. Type m -> Maybe EnumType
+isEnumType (NamedEnumType outputType) = Just outputType
+isEnumType (NonNullEnumType outputType) = Just outputType
+isEnumType _ = Nothing
+
+isInterfaceType :: forall m. Type m -> Maybe (InterfaceType m)
+isInterfaceType (NamedInterfaceType interfaceType) = Just interfaceType
+isInterfaceType (NonNullInterfaceType interfaceType) = Just interfaceType
+isInterfaceType _ = Nothing
+
+isUnionType :: forall m. Type m -> Maybe (UnionType m)
+isUnionType (NamedUnionType unionType) = Just unionType
+isUnionType (NonNullUnionType unionType) = Just unionType
+isUnionType _ = Nothing
+
+isListType :: forall m. Type m -> Maybe (Type m)
+isListType (ListType outputType) = Just outputType
+isListType (NonNullListType outputType) = Just outputType
+isListType _ = Nothing
+
+-- | Checks whether the given output type is a non-null type.
+isNonNullType :: forall m. Type m -> Bool
+isNonNullType (NonNullScalarType _) = True
+isNonNullType (NonNullEnumType _) = True
+isNonNullType (NonNullObjectType _) = True
+isNonNullType (NonNullInterfaceType _) = True
+isNonNullType (NonNullUnionType _) = True
+isNonNullType (NonNullListType _) = True
+isNonNullType _ = False
+
+-- | Resolution context holds resolver arguments and the root value.
+data Context = Context
+    { arguments :: Arguments
+    , values :: Value
+    }
+
+-- | Monad transformer stack used by the resolvers for determining the resolved
+-- value of a field.
+type Resolve m = ReaderT Context m Value
+
+-- | Monad transformer stack used by the resolvers for determining the resolved
+-- event stream of a subscription field.
+type Subscribe m = ReaderT Context m (SourceEventStream m)
+
+-- | A source stream represents the sequence of events, each of which will
+-- trigger a GraphQL execution corresponding to that event.
+type SourceEventStream m = ConduitT () Value m ()
+
+-- | 'Resolver' associates some function(s) with each 'Field'. 'ValueResolver'
+-- resolves a 'Field' into a 'Value'. 'EventStreamResolver' resolves
+-- additionally a 'Field' into a 'SourceEventStream' if it is the field of a
+-- root subscription type.
+--
+-- The resolvers aren't part of the 'Field' itself because not all fields
+-- have resolvers (interface fields don't have an implementation).
+data Resolver m
+    = ValueResolver (Field m) (Resolve m)
+    | EventStreamResolver (Field m) (Resolve m) (Subscribe m)
+
+-- | Retrieves an argument by its name. If the argument with this name couldn't
+-- be found, returns 'Null' (i.e. the argument is assumed to
+-- be optional then).
+argument :: Monad m => Name -> Resolve m
+argument argumentName = do
+    argumentValue <- asks $ lookupArgument . arguments
+    pure $ fromMaybe Null argumentValue
+  where
+    lookupArgument (Arguments argumentMap) =
+        HashMap.lookup argumentName argumentMap

src/Language/GraphQL/Type/Schema.hs

@@ -0,0 +1,219 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+-- | This module provides a representation of a @GraphQL@ Schema in addition to
+-- functions for defining and manipulating schemas.
+module Language.GraphQL.Type.Schema
+    ( schema
+    , schemaWithTypes
+    , module Language.GraphQL.Type.Internal
+    ) where
+
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.Text (Text)
+import Language.GraphQL.AST.DirectiveLocation (DirectiveLocation(..))
+import qualified Language.GraphQL.AST.DirectiveLocation as DirectiveLocation
+import qualified Language.GraphQL.AST as Full
+import Language.GraphQL.Type.Internal
+    ( Directive(..)
+    , Directives
+    , Schema
+    , Type(..)
+    , description
+    , directives
+    , implementations
+    , mutation
+    , subscription
+    , query
+    , types
+    )
+import qualified Language.GraphQL.Type.Definition as Definition
+import qualified Language.GraphQL.Type.Internal as Internal
+import qualified Language.GraphQL.Type.In as In
+import qualified Language.GraphQL.Type.Out as Out
+
+-- | Schema constructor.
+--
+-- __Note:__ When the schema is constructed, by default only the types that
+-- are reachable by traversing the root types are included, other types must
+-- be explicitly referenced using 'schemaWithTypes' instead.
+schema :: forall m
+    . Out.ObjectType m -- ^ Query type.
+    -> Maybe (Out.ObjectType m) -- ^ Mutation type.
+    -> Maybe (Out.ObjectType m) -- ^ Subscription type.
+    -> Directives -- ^ Directive definitions.
+    -> Schema m -- ^ Schema.
+schema queryRoot mutationRoot subscriptionRoot =
+    schemaWithTypes Nothing queryRoot mutationRoot subscriptionRoot mempty
+
+-- | Constructs a complete schema, including user-defined types not referenced
+-- in the schema directly (for example interface implementations).
+schemaWithTypes :: forall m
+    . Maybe Text -- ^ Schema description
+    -> Out.ObjectType m -- ^ Query type.
+    -> Maybe (Out.ObjectType m) -- ^ Mutation type.
+    -> Maybe (Out.ObjectType m) -- ^ Subscription type.
+    -> [Type m] -- ^ Additional types.
+    -> Directives -- ^ Directive definitions.
+    -> Schema m -- ^ Schema.
+schemaWithTypes description' queryRoot mutationRoot subscriptionRoot types' directiveDefinitions =
+    Internal.Schema description' queryRoot mutationRoot subscriptionRoot
+        allDirectives collectedTypes collectedImplementations
+  where
+    allTypes = foldr addTypeDefinition HashMap.empty types'
+    addTypeDefinition type'@(ScalarType (Definition.ScalarType typeName _)) accumulator =
+        HashMap.insert typeName type' accumulator
+    addTypeDefinition type'@(EnumType (Definition.EnumType typeName _ _)) accumulator =
+        HashMap.insert typeName type' accumulator
+    addTypeDefinition type'@(ObjectType (Out.ObjectType typeName _ _ _)) accumulator =
+        HashMap.insert typeName type' accumulator
+    addTypeDefinition type'@(InputObjectType (In.InputObjectType typeName _ _)) accumulator =
+        HashMap.insert typeName type' accumulator
+    addTypeDefinition type'@(InterfaceType (Out.InterfaceType typeName _ _ _)) accumulator =
+        HashMap.insert typeName type' accumulator
+    addTypeDefinition type'@(UnionType (Out.UnionType typeName _ _)) accumulator =
+        HashMap.insert typeName type' accumulator
+    collectedTypes = collectReferencedTypes queryRoot mutationRoot subscriptionRoot allTypes
+    collectedImplementations = collectImplementations collectedTypes
+    allDirectives = HashMap.union directiveDefinitions defaultDirectives
+    defaultDirectives = HashMap.fromList
+        [ ("skip", skipDirective)
+        , ("include", includeDirective)
+        , ("deprecated", deprecatedDirective)
+        , ("specifiedBy", specifiedByDirective)
+        ]
+    includeDirective =
+        Directive includeDescription includeArguments False skipIncludeLocations
+    includeArguments = HashMap.singleton "if"
+        $ In.Argument (Just "Included when true.") ifType Nothing
+    includeDescription = Just
+        "Directs the executor to include this field or fragment only when the \
+        \`if` argument is true."
+    skipDirective = Directive skipDescription skipArguments False skipIncludeLocations
+    skipArguments = HashMap.singleton "if"
+        $ In.Argument (Just "skipped when true.") ifType Nothing
+    ifType = In.NonNullScalarType Definition.boolean
+    skipDescription = Just
+        "Directs the executor to skip this field or fragment when the `if` \
+        \argument is true."
+    skipIncludeLocations =
+        [ ExecutableDirectiveLocation DirectiveLocation.Field
+        , ExecutableDirectiveLocation DirectiveLocation.FragmentSpread
+        , ExecutableDirectiveLocation DirectiveLocation.InlineFragment
+        ]
+    deprecatedDirective =
+        Directive deprecatedDescription deprecatedArguments False deprecatedLocations
+    reasonDescription = Just
+        "Explains why this element was deprecated, usually also including a \
+        \suggestion for how to access supported similar data. Formatted using \
+        \the Markdown syntax, as specified by \
+        \[CommonMark](https://commonmark.org/).'"
+    deprecatedArguments = HashMap.singleton "reason"
+        $ In.Argument reasonDescription (In.NamedScalarType Definition.string)
+        $ Just "No longer supported"
+    deprecatedDescription = Just
+        "Marks an element of a GraphQL schema as no longer supported."
+    deprecatedLocations =
+        [ TypeSystemDirectiveLocation DirectiveLocation.FieldDefinition
+        , TypeSystemDirectiveLocation DirectiveLocation.ArgumentDefinition
+        , TypeSystemDirectiveLocation DirectiveLocation.InputFieldDefinition
+        , TypeSystemDirectiveLocation DirectiveLocation.EnumValue
+        ]
+    specifiedByDirective =
+        Directive specifiedByDescription specifiedByArguments False specifiedByLocations
+    urlDescription = Just
+        "The URL that specifies the behavior of this scalar."
+    specifiedByArguments = HashMap.singleton "url"
+        $ In.Argument urlDescription (In.NonNullScalarType Definition.string) Nothing
+    specifiedByDescription = Just
+        "Exposes a URL that specifies the behavior of this scalar."
+    specifiedByLocations =
+        [TypeSystemDirectiveLocation DirectiveLocation.Scalar]
+
+-- | Traverses the schema and finds all referenced types.
+collectReferencedTypes :: forall m
+    . Out.ObjectType m
+    -> Maybe (Out.ObjectType m)
+    -> Maybe (Out.ObjectType m)
+    -> HashMap Full.Name (Type m)
+    -> HashMap Full.Name (Type m)
+collectReferencedTypes queryRoot mutationRoot subscriptionRoot extraTypes =
+    let queryTypes = traverseObjectType queryRoot extraTypes
+        mutationTypes = maybe queryTypes (`traverseObjectType` queryTypes)
+            mutationRoot
+     in maybe mutationTypes (`traverseObjectType` mutationTypes) subscriptionRoot
+  where
+    collect traverser typeName element foundTypes
+        | HashMap.member typeName foundTypes = foundTypes
+        | otherwise = traverser $ HashMap.insert typeName element foundTypes
+    visitFields (Out.Field _ outputType arguments) foundTypes
+        = traverseOutputType outputType
+        $ foldr visitArguments foundTypes arguments
+    visitArguments (In.Argument _ inputType _) = traverseInputType inputType
+    visitInputFields (In.InputField _ inputType _) = traverseInputType inputType
+    getField (Out.ValueResolver field _) = field
+    getField (Out.EventStreamResolver field _ _) = field
+    traverseInputType (In.InputObjectBaseType objectType) =
+        let In.InputObjectType typeName _ inputFields = objectType
+            element = InputObjectType objectType
+            traverser = flip (foldr visitInputFields) inputFields
+         in collect traverser typeName element
+    traverseInputType (In.ListBaseType listType) =
+        traverseInputType listType
+    traverseInputType (In.ScalarBaseType scalarType) =
+        let Definition.ScalarType typeName _ = scalarType
+         in collect Prelude.id typeName (ScalarType scalarType)
+    traverseInputType (In.EnumBaseType enumType) =
+        let Definition.EnumType typeName _ _ = enumType
+         in collect Prelude.id typeName (EnumType enumType)
+    traverseOutputType (Out.ObjectBaseType objectType) =
+        traverseObjectType objectType
+    traverseOutputType (Out.InterfaceBaseType interfaceType) =
+        traverseInterfaceType interfaceType
+    traverseOutputType (Out.UnionBaseType unionType) =
+        let Out.UnionType typeName _ types' = unionType
+            traverser = flip (foldr traverseObjectType) types'
+         in collect traverser typeName (UnionType unionType)
+    traverseOutputType (Out.ListBaseType listType) =
+        traverseOutputType listType
+    traverseOutputType (Out.ScalarBaseType scalarType) =
+        let Definition.ScalarType typeName _ = scalarType
+         in collect Prelude.id typeName (ScalarType scalarType)
+    traverseOutputType (Out.EnumBaseType enumType) =
+        let Definition.EnumType typeName _ _ = enumType
+         in collect Prelude.id typeName (EnumType enumType)
+    traverseObjectType objectType foundTypes =
+        let Out.ObjectType typeName _ interfaces fields = objectType
+            element = ObjectType objectType
+            traverser = polymorphicTraverser interfaces (getField <$> fields)
+         in collect traverser typeName element foundTypes
+    traverseInterfaceType interfaceType foundTypes =
+        let Out.InterfaceType typeName _ interfaces fields = interfaceType
+            element = InterfaceType interfaceType
+            traverser = polymorphicTraverser interfaces fields
+         in collect traverser typeName element foundTypes
+    polymorphicTraverser interfaces fields
+        = flip (foldr visitFields) fields
+        . flip (foldr traverseInterfaceType) interfaces
+
+-- | Looks for objects and interfaces under the schema types and collects the
+-- interfaces they implement.
+collectImplementations :: forall m
+    . HashMap Full.Name (Type m)
+    -> HashMap Full.Name [Type m]
+collectImplementations = HashMap.foldr go HashMap.empty
+  where
+    go implementation@(InterfaceType interfaceType) accumulator =
+        let Out.InterfaceType _ _ interfaces _ = interfaceType
+         in foldr (add implementation) accumulator interfaces
+    go implementation@(ObjectType objectType) accumulator =
+        let Out.ObjectType _ _ interfaces _ = objectType
+         in foldr (add implementation) accumulator interfaces
+    go _ accumulator = accumulator
+    add implementation (Out.InterfaceType typeName _ _ _) =
+        HashMap.insertWith (++) typeName [implementation]

src/Language/GraphQL/Validate.hs

@@ -0,0 +1,485 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+-- | GraphQL validator.
+module Language.GraphQL.Validate
+    ( Validation.Error(..)
+    , document
+    , module Language.GraphQL.Validate.Rules
+    ) where
+
+import Control.Monad (join)
+import Control.Monad.Trans.Class (MonadTrans(..))
+import Control.Monad.Trans.Reader (runReaderT)
+import Data.Foldable (toList)
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.Sequence (Seq(..), (><), (|>))
+import qualified Data.Sequence as Seq
+import Language.GraphQL.AST.DirectiveLocation (DirectiveLocation(..))
+import qualified Language.GraphQL.AST.DirectiveLocation as DirectiveLocation
+import qualified Language.GraphQL.AST.Document as Full
+import qualified Language.GraphQL.Type.Internal as Type
+import qualified Language.GraphQL.Type.In as In
+import qualified Language.GraphQL.Type.Out as Out
+import Language.GraphQL.Type.Schema (Schema)
+import qualified Language.GraphQL.Type.Schema as Schema
+import Language.GraphQL.Validate.Rules
+import Language.GraphQL.Validate.Validation (Validation(Validation))
+import qualified Language.GraphQL.Validate.Validation as Validation
+
+type ApplySelectionRule m a
+    = HashMap Full.Name (Schema.Type m)
+    -> Validation.Rule m
+    -> Maybe (Out.Type m)
+    -> a
+    -> Seq (Validation.RuleT m)
+
+type ApplyRule m a = Validation.Rule m -> a -> Seq (Validation.RuleT m)
+
+-- | Validates a document and returns a list of found errors. If the returned
+-- list is empty, the document is valid.
+document :: forall m
+    . Schema m
+    -> [Validation.Rule m]
+    -> Full.Document
+    -> Seq Validation.Error
+document schema' rules' document' =
+    runReaderT reader context
+  where
+    context = Validation
+        { Validation.ast = document'
+        , Validation.schema = schema'
+        }
+    reader = do
+        rule' <- lift $ Seq.fromList rules'
+        join $ lift $ foldr (definition rule' context) Seq.empty document'
+
+definition :: Validation.Rule m
+    -> Validation m
+    -> Full.Definition
+    -> Seq (Validation.RuleT m)
+    -> Seq (Validation.RuleT m)
+definition (Validation.DefinitionRule rule) _ definition' accumulator =
+    accumulator |> rule definition'
+definition rule context (Full.ExecutableDefinition definition') accumulator =
+    accumulator >< executableDefinition rule context definition'
+definition rule context (Full.TypeSystemDefinition typeSystemDefinition' _) accumulator =
+    accumulator >< typeSystemDefinition context rule typeSystemDefinition'
+definition rule context (Full.TypeSystemExtension extension _) accumulator =
+    accumulator >< typeSystemExtension context rule extension
+
+typeSystemExtension :: forall m
+    . Validation m
+    -> ApplyRule m Full.TypeSystemExtension
+typeSystemExtension context rule = \case
+    Full.SchemaExtension extension -> schemaExtension context rule extension
+    Full.TypeExtension extension -> typeExtension context rule extension
+
+typeExtension :: forall m. Validation m -> ApplyRule m Full.TypeExtension
+typeExtension context rule = \case
+    Full.ScalarTypeExtension _ directives' ->
+        directives context rule scalarLocation directives'
+    Full.ObjectTypeFieldsDefinitionExtension _ _ directives' fields
+        -> directives context rule objectLocation directives'
+        >< foldMap (fieldDefinition context rule) fields
+    Full.ObjectTypeDirectivesExtension _ _ directives' ->
+        directives context rule objectLocation directives'
+    Full.ObjectTypeImplementsInterfacesExtension _ _ -> mempty
+    Full.InterfaceTypeFieldsDefinitionExtension _ directives' fields
+        -> directives context rule interfaceLocation directives'
+        >< foldMap (fieldDefinition context rule) fields
+    Full.InterfaceTypeDirectivesExtension _ directives' ->
+        directives context rule interfaceLocation directives'
+    Full.UnionTypeUnionMemberTypesExtension _ directives' _ ->
+        directives context rule unionLocation directives'
+    Full.UnionTypeDirectivesExtension _ directives' ->
+        directives context rule unionLocation directives'
+    Full.EnumTypeEnumValuesDefinitionExtension _ directives' values
+        -> directives context rule enumLocation directives'
+        >< foldMap (enumValueDefinition context rule) values
+    Full.EnumTypeDirectivesExtension _ directives' ->
+        directives context rule enumLocation directives'
+    Full.InputObjectTypeInputFieldsDefinitionExtension _ directives' fields
+        -> directives context rule inputObjectLocation directives'
+        >< foldMap forEachInputFieldDefinition fields
+    Full.InputObjectTypeDirectivesExtension _ directives' ->
+        directives context rule inputObjectLocation directives'
+  where
+    forEachInputFieldDefinition =
+        inputValueDefinition context rule inputFieldDefinitionLocation
+
+schemaExtension :: forall m. Validation m -> ApplyRule m Full.SchemaExtension
+schemaExtension context rule = \case
+    Full.SchemaOperationExtension directives' _ ->
+        directives context rule schemaLocation directives'
+    Full.SchemaDirectivesExtension directives' ->
+        directives context rule schemaLocation directives'
+
+schemaLocation :: DirectiveLocation
+schemaLocation = TypeSystemDirectiveLocation DirectiveLocation.Schema
+
+interfaceLocation :: DirectiveLocation
+interfaceLocation = TypeSystemDirectiveLocation DirectiveLocation.Interface
+
+objectLocation :: DirectiveLocation
+objectLocation = TypeSystemDirectiveLocation DirectiveLocation.Object
+
+unionLocation :: DirectiveLocation
+unionLocation = TypeSystemDirectiveLocation DirectiveLocation.Union
+
+enumLocation :: DirectiveLocation
+enumLocation = TypeSystemDirectiveLocation DirectiveLocation.Enum
+
+inputObjectLocation :: DirectiveLocation
+inputObjectLocation = TypeSystemDirectiveLocation DirectiveLocation.InputObject
+
+scalarLocation :: DirectiveLocation
+scalarLocation = TypeSystemDirectiveLocation DirectiveLocation.Scalar
+
+enumValueLocation :: DirectiveLocation
+enumValueLocation = TypeSystemDirectiveLocation DirectiveLocation.EnumValue
+
+fieldDefinitionLocation :: DirectiveLocation
+fieldDefinitionLocation =
+    TypeSystemDirectiveLocation DirectiveLocation.FieldDefinition
+
+inputFieldDefinitionLocation :: DirectiveLocation
+inputFieldDefinitionLocation =
+    TypeSystemDirectiveLocation DirectiveLocation.InputFieldDefinition
+
+argumentDefinitionLocation :: DirectiveLocation
+argumentDefinitionLocation =
+    TypeSystemDirectiveLocation DirectiveLocation.ArgumentDefinition
+
+queryLocation :: DirectiveLocation
+queryLocation = ExecutableDirectiveLocation DirectiveLocation.Query
+
+mutationLocation :: DirectiveLocation
+mutationLocation = ExecutableDirectiveLocation DirectiveLocation.Mutation
+
+subscriptionLocation :: DirectiveLocation
+subscriptionLocation =
+    ExecutableDirectiveLocation DirectiveLocation.Subscription
+
+fieldLocation :: DirectiveLocation
+fieldLocation = ExecutableDirectiveLocation DirectiveLocation.Field
+
+fragmentDefinitionLocation :: DirectiveLocation
+fragmentDefinitionLocation =
+    ExecutableDirectiveLocation DirectiveLocation.FragmentDefinition
+
+fragmentSpreadLocation :: DirectiveLocation
+fragmentSpreadLocation =
+    ExecutableDirectiveLocation DirectiveLocation.FragmentSpread
+
+inlineFragmentLocation :: DirectiveLocation
+inlineFragmentLocation =
+    ExecutableDirectiveLocation DirectiveLocation.InlineFragment
+
+executableDefinition :: forall m
+    . Validation.Rule m
+    -> Validation m
+    -> Full.ExecutableDefinition
+    -> Seq (Validation.RuleT m)
+executableDefinition rule context (Full.DefinitionOperation operation) =
+    operationDefinition rule context operation
+executableDefinition rule context (Full.DefinitionFragment fragment) =
+    fragmentDefinition rule context fragment
+
+typeSystemDefinition :: forall m
+    . Validation m
+    -> ApplyRule m Full.TypeSystemDefinition
+typeSystemDefinition context rule = \case
+    Full.SchemaDefinition directives' _ ->
+        directives context rule schemaLocation directives'
+    Full.TypeDefinition typeDefinition' ->
+        typeDefinition context rule typeDefinition'
+    Full.DirectiveDefinition _ _ arguments' _ _ ->
+        argumentsDefinition context rule arguments'
+
+typeDefinition :: forall m. Validation m -> ApplyRule m Full.TypeDefinition
+typeDefinition context rule = \case
+    Full.ScalarTypeDefinition _ _ directives' ->
+        directives context rule scalarLocation directives'
+    Full.ObjectTypeDefinition _ _ _ directives' fields
+        -> directives context rule objectLocation directives'
+        >< foldMap (fieldDefinition context rule) fields
+    Full.InterfaceTypeDefinition _ _ _ directives' fields
+        -> directives context rule interfaceLocation directives'
+        >< foldMap (fieldDefinition context rule) fields
+    Full.UnionTypeDefinition _ _ directives' _ ->
+        directives context rule unionLocation directives'
+    Full.EnumTypeDefinition _ _ directives' values
+        -> directives context rule enumLocation directives'
+        >< foldMap (enumValueDefinition context rule) values
+    Full.InputObjectTypeDefinition _ _ directives' fields
+        -> directives context rule inputObjectLocation directives'
+        <> foldMap forEachInputFieldDefinition fields
+  where
+    forEachInputFieldDefinition =
+        inputValueDefinition context rule inputFieldDefinitionLocation
+
+enumValueDefinition :: forall m
+    . Validation m
+    -> ApplyRule m Full.EnumValueDefinition
+enumValueDefinition context rule (Full.EnumValueDefinition _ _ directives') =
+    directives context rule enumValueLocation directives'
+
+fieldDefinition :: forall m. Validation m -> ApplyRule m Full.FieldDefinition
+fieldDefinition context rule (Full.FieldDefinition _ _ arguments' _ directives')
+    = directives context rule fieldDefinitionLocation directives'
+    >< argumentsDefinition context rule arguments'
+
+argumentsDefinition :: forall m
+    . Validation m
+    -> ApplyRule m Full.ArgumentsDefinition
+argumentsDefinition context rule (Full.ArgumentsDefinition definitions) =
+    foldMap forEachArgument definitions
+  where
+    forEachArgument =
+        inputValueDefinition context rule argumentDefinitionLocation
+
+inputValueDefinition :: forall m
+    . Validation m
+    -> Validation.Rule m
+    -> DirectiveLocation
+    -> Full.InputValueDefinition
+    -> Seq (Validation.RuleT m)
+inputValueDefinition context rule directiveLocation definition' =
+    let Full.InputValueDefinition _ _ _ _ directives' = definition'
+     in directives context rule directiveLocation directives'
+
+operationDefinition :: forall m
+    . Validation.Rule m
+    -> Validation m
+    -> Full.OperationDefinition
+    -> Seq (Validation.RuleT m)
+operationDefinition rule context operation
+    | Validation.OperationDefinitionRule operationRule <- rule =
+        pure $ operationRule operation
+    | Validation.VariablesRule variablesRule <- rule
+    , Full.OperationDefinition _ _ variables _ _ _ <- operation =
+        foldMap (variableDefinition context rule) variables |> variablesRule variables
+    | Full.SelectionSet selections _ <- operation =
+        selectionSet context types' rule queryRoot selections
+    | Full.OperationDefinition Full.Query _ _ directives' selections _  <- operation
+        = selectionSet context types' rule queryRoot selections
+        >< directives context rule queryLocation directives'
+    | Full.OperationDefinition Full.Mutation _ _ directives' selections _  <- operation =
+        let root = Out.NamedObjectType <$> Schema.mutation schema'
+         in selectionSet context types' rule root selections
+        >< directives context rule mutationLocation directives'
+    | Full.OperationDefinition Full.Subscription _ _ directives' selections _  <- operation =
+        let root = Out.NamedObjectType <$> Schema.subscription schema'
+         in selectionSet context types' rule root selections
+        >< directives context rule subscriptionLocation directives'
+  where
+    schema' = Validation.schema context
+    queryRoot = Just $ Out.NamedObjectType $ Schema.query schema'
+    types' = Schema.types schema'
+
+typeToOut :: forall m. Schema.Type m -> Maybe (Out.Type m)
+typeToOut (Schema.ObjectType objectType) =
+    Just $ Out.NamedObjectType objectType
+typeToOut (Schema.InterfaceType interfaceType) =
+    Just $ Out.NamedInterfaceType interfaceType
+typeToOut (Schema.UnionType unionType) = Just $ Out.NamedUnionType unionType
+typeToOut (Schema.EnumType enumType) = Just $ Out.NamedEnumType enumType
+typeToOut (Schema.ScalarType scalarType) = Just $ Out.NamedScalarType scalarType
+typeToOut _ = Nothing
+
+variableDefinition :: forall m
+    . Validation m
+    -> ApplyRule m Full.VariableDefinition
+variableDefinition context rule (Full.VariableDefinition _ typeName value' _)
+    | Just defaultValue' <- value'
+    , types <- Schema.types $ Validation.schema context
+    , variableType <- Type.lookupInputType typeName types =
+        constValue rule variableType defaultValue'
+variableDefinition _ _ _ = mempty
+
+constValue :: forall m
+    . Validation.Rule m
+    -> Maybe In.Type
+    -> Full.Node Full.ConstValue
+    -> Seq (Validation.RuleT m)
+constValue (Validation.ValueRule _ rule) valueType = go valueType
+  where
+    go inputObjectType value'@(Full.Node (Full.ConstObject fields) _)
+        = foldMap (forEach inputObjectType) (Seq.fromList fields)
+        |> rule inputObjectType value'
+    go anotherValue value' = pure $ rule anotherValue value'
+    forEach inputObjectType Full.ObjectField{value = value', ..} =
+        go (valueTypeByName name inputObjectType) value'
+constValue _ _ = const mempty
+
+inputFieldType :: In.InputField -> In.Type
+inputFieldType (In.InputField _ inputFieldType' _) = inputFieldType'
+
+valueTypeByName :: Full.Name -> Maybe In.Type -> Maybe In.Type
+valueTypeByName fieldName (Just( In.InputObjectBaseType inputObjectType)) =
+    let In.InputObjectType _ _ fieldTypes = inputObjectType
+     in inputFieldType <$> HashMap.lookup fieldName fieldTypes
+valueTypeByName _ _ = Nothing
+
+fragmentDefinition :: forall m
+    . Validation.Rule m
+    -> Validation m
+    -> Full.FragmentDefinition
+    -> Seq (Validation.RuleT m)
+fragmentDefinition (Validation.FragmentDefinitionRule rule) _ definition' =
+    pure $ rule definition'
+fragmentDefinition rule context definition'
+    | Full.FragmentDefinition _ typeCondition directives' selections _ <- definition'
+    , Validation.FragmentRule definitionRule _ <- rule
+        = applyToChildren typeCondition directives' selections
+        |> definitionRule definition'
+    | Full.FragmentDefinition _ typeCondition directives' selections _ <- definition'
+        = applyToChildren typeCondition directives' selections
+  where
+    types' = Schema.types $ Validation.schema context
+    applyToChildren typeCondition directives' selections
+        = selectionSet context types' rule (lookupType' typeCondition) selections
+        >< directives context rule fragmentDefinitionLocation directives'
+    lookupType' = flip lookupType types'
+
+lookupType :: forall m
+    . Full.TypeCondition
+    -> HashMap Full.Name (Schema.Type m)
+    -> Maybe (Out.Type m)
+lookupType typeCondition types' = HashMap.lookup typeCondition types'
+    >>= typeToOut
+
+selectionSet :: Traversable t
+    => forall m
+    . Validation m
+    -> ApplySelectionRule m (t Full.Selection)
+selectionSet context types' rule = foldMap . selection context types' rule
+
+selection :: forall m. Validation m -> ApplySelectionRule m Full.Selection
+selection context types' rule objectType selection'
+    | Validation.SelectionRule selectionRule <- rule =
+        applyToChildren |> selectionRule objectType selection'
+    | otherwise = applyToChildren
+  where
+    applyToChildren =
+        case selection' of
+            Full.FieldSelection field' ->
+                field context types' rule objectType field'
+            Full.InlineFragmentSelection inlineFragment' ->
+                inlineFragment context types' rule objectType inlineFragment'
+            Full.FragmentSpreadSelection fragmentSpread' ->
+                fragmentSpread context rule fragmentSpread'
+
+field :: forall m. Validation m -> ApplySelectionRule m Full.Field
+field context types' rule objectType field' = go field'
+  where
+    go (Full.Field _ fieldName _ _ _ _)
+        | Validation.FieldRule fieldRule <- rule =
+            applyToChildren fieldName |> fieldRule objectType field'
+        | Validation.ArgumentsRule argumentsRule _  <- rule =
+            applyToChildren fieldName |> argumentsRule objectType field'
+        | otherwise = applyToChildren fieldName
+    typeFieldType (Out.Field _ type' _) = type'
+    typeFieldArguments (Out.Field _ _ argumentTypes) = argumentTypes
+    applyToChildren fieldName =
+        let Full.Field _ _ arguments' directives' selections _ = field'
+            typeField = objectType >>= Type.lookupTypeField fieldName
+            argumentTypes = maybe mempty typeFieldArguments typeField
+         in selectionSet context types' rule (typeFieldType <$> typeField) selections
+            >< directives context rule fieldLocation directives'
+            >< arguments rule argumentTypes arguments'
+
+arguments :: forall m
+    . Validation.Rule m
+    -> In.Arguments
+    -> [Full.Argument]
+    -> Seq (Validation.RuleT m)
+arguments rule argumentTypes = foldMap forEach . Seq.fromList
+  where
+    forEach argument'@(Full.Argument argumentName _ _) =
+       let argumentType = HashMap.lookup argumentName argumentTypes
+        in argument rule argumentType argument'
+
+argument :: forall m
+    . Validation.Rule m
+    -> Maybe In.Argument
+    -> Full.Argument
+    -> Seq (Validation.RuleT m)
+argument rule argumentType (Full.Argument _ value' _) =
+    value rule (valueType <$> argumentType) value'
+  where
+    valueType (In.Argument _ valueType' _) = valueType'
+
+value :: forall m
+    . Validation.Rule m
+    -> Maybe In.Type
+    -> Full.Node Full.Value
+    -> Seq (Validation.RuleT m)
+value (Validation.ValueRule rule _) valueType = go valueType
+  where
+    go inputObjectType value'@(Full.Node (Full.Object fields) _)
+        = foldMap (forEach inputObjectType) (Seq.fromList fields)
+        |> rule inputObjectType value'
+    go anotherValue value' = pure $ rule anotherValue value'
+    forEach inputObjectType Full.ObjectField{value = value', ..} =
+        go (valueTypeByName name inputObjectType) value'
+value _ _ = const mempty
+
+inlineFragment :: forall m
+    . Validation m
+    -> ApplySelectionRule m Full.InlineFragment
+inlineFragment context types' rule objectType inlineFragment' =
+    go inlineFragment'
+  where
+    go (Full.InlineFragment optionalType directives' selections _)
+        | Validation.FragmentRule _ fragmentRule <- rule
+            = applyToChildren (refineTarget optionalType) directives' selections
+            |> fragmentRule inlineFragment'
+        | otherwise = applyToChildren (refineTarget optionalType) directives' selections
+    refineTarget (Just typeCondition) = lookupType typeCondition types'
+    refineTarget Nothing = objectType
+    applyToChildren objectType' directives' selections
+        = selectionSet context types' rule objectType' selections
+        >< directives context rule inlineFragmentLocation directives'
+
+fragmentSpread :: forall m. Validation m -> ApplyRule m Full.FragmentSpread
+fragmentSpread context rule fragmentSpread'@(Full.FragmentSpread _ directives' _)
+    | Validation.FragmentSpreadRule fragmentRule <- rule =
+        applyToChildren |> fragmentRule fragmentSpread'
+    | otherwise = applyToChildren
+  where
+    applyToChildren = directives context rule fragmentSpreadLocation directives'
+
+directives :: Traversable t
+    => forall m
+    . Validation m
+    -> Validation.Rule m
+    -> DirectiveLocation
+    -> t Full.Directive
+    -> Seq (Validation.RuleT m)
+directives context rule directiveLocation directives'
+    | Validation.DirectivesRule directivesRule <- rule =
+        applyToChildren |> directivesRule directiveLocation directiveList
+    | otherwise = applyToChildren
+  where
+    directiveList = toList directives'
+    applyToChildren = foldMap (directive context rule) directiveList
+
+directive :: forall m. Validation m -> ApplyRule m Full.Directive
+directive _ (Validation.ArgumentsRule _ argumentsRule) directive' =
+    pure $ argumentsRule directive'
+directive context rule (Full.Directive directiveName arguments' _) =
+    let argumentTypes = maybe HashMap.empty directiveArguments
+            $ HashMap.lookup directiveName
+            $ Schema.directives
+            $ Validation.schema context
+     in arguments rule argumentTypes arguments'
+  where
+    directiveArguments (Schema.Directive _ argumentTypes _ _) = argumentTypes

src/Language/GraphQL/Validate/Validation.hs

@@ -0,0 +1,50 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+-- | Definitions used by the validation rules and the validator itself.
+module Language.GraphQL.Validate.Validation
+    ( Error(..)
+    , Rule(..)
+    , RuleT
+    , Validation(..)
+    ) where
+
+import Control.Monad.Trans.Reader (ReaderT)
+import Data.Sequence (Seq)
+import Language.GraphQL.AST.DirectiveLocation (DirectiveLocation(..))
+import Language.GraphQL.AST.Document
+import qualified Language.GraphQL.Type.In as In
+import qualified Language.GraphQL.Type.Out as Out
+import Language.GraphQL.Type.Schema (Schema)
+
+-- | Validation error.
+data Error = Error
+    { message :: String
+    , locations :: [Location]
+    } deriving (Eq, Show)
+
+-- | Validation rule context.
+data Validation m = Validation
+    { ast :: Document
+    , schema :: Schema m
+    }
+
+-- | 'Rule' assigns a function to each AST node that can be validated. If the
+-- validation fails, the function should return an error message, or 'Nothing'
+-- otherwise.
+data Rule m
+    = DefinitionRule (Definition -> RuleT m)
+    | OperationDefinitionRule (OperationDefinition -> RuleT m)
+    | FragmentDefinitionRule (FragmentDefinition -> RuleT m)
+    | SelectionRule (Maybe (Out.Type m) -> Selection -> RuleT m)
+    | FragmentRule (FragmentDefinition -> RuleT m) (InlineFragment -> RuleT m)
+    | FragmentSpreadRule (FragmentSpread -> RuleT m)
+    | FieldRule (Maybe (Out.Type m) -> Field -> RuleT m)
+    | ArgumentsRule (Maybe (Out.Type m) -> Field -> RuleT m) (Directive -> RuleT m)
+    | DirectivesRule (DirectiveLocation -> [Directive] -> RuleT m)
+    | VariablesRule ([VariableDefinition] -> RuleT m)
+    | ValueRule (Maybe In.Type -> Node Value -> RuleT m) (Maybe In.Type -> Node ConstValue -> RuleT m)
+
+-- | Monad transformer used by the rules.
+type RuleT m = ReaderT (Validation m) Seq Error

stack.yaml

@@ -1,5 +0,0 @@
-flags: {}
-packages:
-- '.'
-extra-deps: []
-resolver: lts-3.4

tests/Language/GraphQL/AST/Arbitrary.hs

@@ -0,0 +1,130 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Language.GraphQL.AST.Arbitrary
+    ( AnyArgument(..)
+    , AnyLocation(..)
+    , AnyName(..)
+    , AnyNode(..)
+    , AnyObjectField(..)
+    , AnyValue(..)
+    , printArgument
+    ) where
+
+import qualified Language.GraphQL.AST.Document as Doc
+import Test.QuickCheck.Arbitrary (Arbitrary (arbitrary))
+import Test.QuickCheck (oneof, elements, listOf, resize, NonEmptyList (..))
+import Test.QuickCheck.Gen (Gen (..))
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Data.Functor ((<&>))
+
+newtype AnyPrintableChar = AnyPrintableChar
+    { getAnyPrintableChar :: Char
+    } deriving (Eq, Show)
+
+alpha :: String
+alpha = ['a'..'z'] <> ['A'..'Z']
+
+num :: String
+num = ['0'..'9']
+
+instance Arbitrary AnyPrintableChar where
+    arbitrary = AnyPrintableChar <$> elements chars
+        where
+           chars = alpha <> num <> ['_']
+
+newtype AnyPrintableText = AnyPrintableText
+    { getAnyPrintableText :: Text
+    } deriving (Eq, Show)
+
+instance Arbitrary AnyPrintableText where
+    arbitrary = do
+        nonEmptyStr <- getNonEmpty <$> (arbitrary :: Gen (NonEmptyList AnyPrintableChar))
+        pure $ AnyPrintableText
+            $ Text.pack
+            $ map getAnyPrintableChar nonEmptyStr
+
+-- https://spec.graphql.org/June2018/#Name
+newtype AnyName = AnyName
+    { getAnyName :: Text
+    } deriving (Eq, Show)
+
+instance Arbitrary AnyName where
+    arbitrary = do
+        firstChar <- elements $ alpha <> ['_']
+        rest <- (arbitrary :: Gen [AnyPrintableChar])
+        pure $ AnyName
+            $ Text.pack
+            $ firstChar : map getAnyPrintableChar rest
+
+newtype AnyLocation = AnyLocation
+    { getAnyLocation :: Doc.Location
+    } deriving (Eq, Show)
+
+instance Arbitrary AnyLocation where
+    arbitrary = AnyLocation <$> (Doc.Location <$> arbitrary <*> arbitrary)
+
+newtype AnyNode a = AnyNode
+    { getAnyNode :: Doc.Node a
+    } deriving (Eq, Show)
+
+instance Arbitrary a => Arbitrary (AnyNode a) where
+    arbitrary = do
+        (AnyLocation location') <- arbitrary
+        node' <- flip Doc.Node location' <$> arbitrary
+        pure $ AnyNode node'
+
+newtype AnyObjectField a = AnyObjectField
+    { getAnyObjectField :: Doc.ObjectField a
+    } deriving (Eq, Show)
+
+instance Arbitrary a => Arbitrary (AnyObjectField a) where
+    arbitrary = do
+        name' <- getAnyName <$> arbitrary
+        value' <- getAnyNode <$> arbitrary
+        location' <- getAnyLocation <$> arbitrary
+        pure $ AnyObjectField $ Doc.ObjectField name' value' location'
+
+newtype AnyValue = AnyValue
+    { getAnyValue :: Doc.Value
+    } deriving (Eq, Show)
+
+instance Arbitrary AnyValue
+  where
+    arbitrary =
+        let variableGen :: Gen Doc.Value
+            variableGen = Doc.Variable . getAnyName <$> arbitrary
+            listGen :: Gen [Doc.Node Doc.Value]
+            listGen = (resize 5 . listOf) nodeGen
+            nodeGen :: Gen (Doc.Node Doc.Value)
+            nodeGen = fmap getAnyNode arbitrary <&> fmap getAnyValue
+            objectGen :: Gen [Doc.ObjectField Doc.Value]
+            objectGen = resize 1
+                $ fmap getNonEmpty arbitrary
+                <&> map (fmap getAnyValue . getAnyObjectField)
+         in AnyValue <$> oneof
+            [ variableGen
+            , Doc.Int <$> arbitrary
+            , Doc.Float <$> arbitrary
+            , Doc.String . getAnyPrintableText <$> arbitrary
+            , Doc.Boolean <$> arbitrary
+            , MkGen $ \_ _ -> Doc.Null
+            , Doc.Enum . getAnyName <$> arbitrary
+            , Doc.List <$> listGen
+            , Doc.Object <$> objectGen
+            ]
+
+newtype AnyArgument a = AnyArgument
+    { getAnyArgument :: Doc.Argument
+    } deriving (Eq, Show)
+
+instance Arbitrary a => Arbitrary (AnyArgument a) where
+    arbitrary = do
+        name' <- getAnyName <$> arbitrary
+        (AnyValue value') <- arbitrary
+        (AnyLocation location') <- arbitrary
+        pure $ AnyArgument $ Doc.Argument name' (Doc.Node value' location') location'
+
+printArgument :: AnyArgument AnyValue -> Text
+printArgument (AnyArgument (Doc.Argument name' (Doc.Node value' _) _)) =
+    name' <> ": " <> (Text.pack . show) value'

tests/Language/GraphQL/AST/DocumentSpec.hs

@@ -0,0 +1,26 @@
+{-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE OverloadedStrings #-}
+module Language.GraphQL.AST.DocumentSpec
+    ( spec
+    ) where
+
+import Language.GraphQL.AST.Document
+import Test.Hspec (Spec, describe, it, shouldBe)
+
+spec :: Spec
+spec = do
+    describe "Document" $ do
+        it "shows objects" $
+            let zero = Location 0 0
+                object = ConstObject
+                    [ ObjectField "field1" (Node (ConstFloat 1.2) zero) zero
+                    , ObjectField "field2" (Node ConstNull zero) zero
+                    ]
+                expected = "{ field1: 1.2, field2: null }"
+             in show object `shouldBe` expected
+
+    describe "Description" $
+        it "keeps content when merging with no description" $
+            let expected = Description $ Just "Left description"
+                actual = expected <> Description Nothing
+             in actual `shouldBe` expected

tests/Language/GraphQL/AST/EncoderSpec.hs

@@ -0,0 +1,254 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Language.GraphQL.AST.EncoderSpec
+    ( spec
+    ) where
+
+import Data.List.NonEmpty (NonEmpty(..))
+import qualified Language.GraphQL.AST.Document as Full
+import Language.GraphQL.AST.Encoder
+import Test.Hspec (Spec, context, describe, it, shouldBe, shouldStartWith, shouldEndWith, shouldNotContain)
+import Test.QuickCheck (choose, oneof, forAll)
+import qualified Data.Text.Lazy as Text.Lazy
+import qualified Language.GraphQL.AST.DirectiveLocation as DirectiveLocation
+
+spec :: Spec
+spec = do
+    describe "value" $ do
+        context "minified" $ do
+            it "encodes null" $
+                value minified Full.Null `shouldBe` "null"
+            it "escapes \\" $
+                value minified (Full.String "\\") `shouldBe` "\"\\\\\""
+            it "escapes double quotes" $
+                value minified (Full.String "\"") `shouldBe` "\"\\\"\""
+            it "escapes \\f" $
+                value minified (Full.String "\f") `shouldBe` "\"\\f\""
+            it "escapes \\n" $
+                value minified (Full.String "\n") `shouldBe` "\"\\n\""
+            it "escapes \\r" $
+                value minified (Full.String "\r") `shouldBe` "\"\\r\""
+            it "escapes \\t" $
+                value minified (Full.String "\t") `shouldBe` "\"\\t\""
+            it "escapes backspace" $
+                value minified (Full.String "a\bc") `shouldBe` "\"a\\bc\""
+            context "escapes Unicode for chars less than 0010" $ do
+                it "Null" $ value minified (Full.String "\x0000") `shouldBe` "\"\\u0000\""
+                it "bell" $ value minified (Full.String "\x0007") `shouldBe` "\"\\u0007\""
+            context "escapes Unicode for char less than 0020" $ do
+                it "DLE" $ value minified (Full.String "\x0010") `shouldBe` "\"\\u0010\""
+                it "EM" $ value minified (Full.String "\x0019") `shouldBe` "\"\\u0019\""
+            context "encodes without escape" $ do
+                it "space" $ value minified (Full.String "\x0020") `shouldBe` "\" \""
+                it "~" $ value minified (Full.String "\x007E") `shouldBe` "\"~\""
+
+        context "pretty" $ do
+            it "encodes null" $
+                value pretty Full.Null `shouldBe` "null"
+
+            it "uses strings for short string values" $
+                value pretty (Full.String "Short text") `shouldBe` "\"Short text\""
+            it "uses block strings for text with new lines, with newline symbol" $
+                let expected = "\"\"\"\n\
+                        \  Line 1\n\
+                        \  Line 2\n\
+                        \\"\"\""
+                    actual = value pretty $ Full.String "Line 1\nLine 2"
+                 in actual `shouldBe` expected
+            it "uses block strings for text with new lines, with CR symbol" $
+                let expected = "\"\"\"\n\
+                        \  Line 1\n\
+                        \  Line 2\n\
+                        \\"\"\""
+                    actual = value pretty $ Full.String "Line 1\rLine 2"
+                 in actual `shouldBe` expected
+            it "uses block strings for text with new lines, with CR symbol followed by newline" $
+                let expected = "\"\"\"\n\
+                        \  Line 1\n\
+                        \  Line 2\n\
+                        \\"\"\""
+                    actual = value pretty $ Full.String "Line 1\r\nLine 2"
+                 in actual `shouldBe` expected
+            it "encodes as one line string if has escaped symbols" $ do
+                let genNotAllowedSymbol = oneof
+                        [ choose ('\x0000', '\x0008')
+                        , choose ('\x000B', '\x000C')
+                        , choose ('\x000E', '\x001F')
+                        , pure '\x007F'
+                        ]
+                forAll genNotAllowedSymbol $ \x -> do
+                    let rawValue = "Short \n" <> Text.Lazy.cons x "text"
+                        encoded = Text.Lazy.unpack
+                            $ value pretty
+                            $ Full.String
+                            $ Text.Lazy.toStrict rawValue
+                    shouldStartWith encoded "\""
+                    shouldEndWith encoded "\""
+                    shouldNotContain encoded "\"\"\""
+
+            it "Hello world" $
+                let actual = value pretty
+                        $ Full.String "Hello,\n  World!\n\nYours,\n  GraphQL."
+                    expected = "\"\"\"\n\
+                        \  Hello,\n\
+                        \    World!\n\
+                        \\n\
+                        \  Yours,\n\
+                        \    GraphQL.\n\
+                        \\"\"\""
+                  in actual `shouldBe` expected
+
+            it "has only newlines" $
+                let actual = value pretty $ Full.String "\n"
+                    expected = "\"\"\"\n\n\n\"\"\""
+                 in actual `shouldBe` expected
+            it "has newlines and one symbol at the begining" $
+                let actual = value pretty $ Full.String "a\n\n"
+                    expected = "\"\"\"\n\
+                        \  a\n\
+                        \\n\
+                        \\n\
+                        \\"\"\""
+                 in actual `shouldBe` expected
+            it "has newlines and one symbol at the end" $
+                let actual = value pretty $ Full.String "\n\na"
+                    expected = "\"\"\"\n\
+                        \\n\
+                        \\n\
+                        \  a\n\
+                        \\"\"\""
+                 in actual `shouldBe` expected
+            it "has newlines and one symbol in the middle" $
+                let actual = value pretty $ Full.String "\na\n"
+                    expected = "\"\"\"\n\
+                        \\n\
+                        \  a\n\
+                        \\n\
+                        \\"\"\""
+                 in actual `shouldBe` expected
+            it "skip trailing whitespaces" $
+                let actual = value pretty $ Full.String "  Short\ntext    "
+                    expected = "\"\"\"\n\
+                        \  Short\n\
+                        \  text\n\
+                        \\"\"\""
+                 in actual `shouldBe` expected
+
+    describe "definition" $
+        it "indents block strings in arguments" $
+            let location = Full.Location 0 0
+                argumentValue = Full.Node (Full.String "line1\nline2") location
+                arguments = [Full.Argument "message" argumentValue location]
+                field = Full.Field Nothing "field" arguments [] [] location
+                fieldSelection = pure $ Full.FieldSelection field
+                operation = Full.DefinitionOperation
+                    $ Full.SelectionSet fieldSelection location
+                expected = "{\n\
+                    \  field(message: \"\"\"\n\
+                    \    line1\n\
+                    \    line2\n\
+                    \  \"\"\")\n\
+                    \}\n"
+                actual = definition pretty operation
+             in actual `shouldBe` expected
+
+    describe "operationType" $
+        it "produces lowercase mutation operation type" $
+            let actual = operationType pretty Full.Mutation
+             in actual `shouldBe` "mutation"
+
+    describe "typeSystemDefinition" $ do
+        it "produces a schema with an indented operation type definition" $
+            let queryType = Full.OperationTypeDefinition Full.Query "QueryRootType"
+                mutationType = Full.OperationTypeDefinition Full.Mutation "MutationType"
+                operations = queryType :| pure mutationType
+                definition' = Full.SchemaDefinition [] operations
+                expected = "schema {\n\
+                    \  query: QueryRootType\n\
+                    \  mutation: MutationType\n\
+                    \}\n"
+                actual = typeSystemDefinition pretty definition'
+             in actual `shouldBe` expected
+
+        it "encodes a scalar type definition" $
+            let uuidType = Full.ScalarTypeDefinition mempty "UUID" mempty
+                definition' = Full.TypeDefinition uuidType
+                expected = "scalar UUID"
+                actual = typeSystemDefinition pretty definition'
+             in actual `shouldBe` expected
+
+        it "encodes an interface definition" $
+            let someType = Full.TypeNamed "String"
+                argument = Full.InputValueDefinition mempty "arg" someType Nothing mempty
+                arguments = Full.ArgumentsDefinition [argument]
+                definition' = Full.TypeDefinition
+                    $ Full.InterfaceTypeDefinition mempty "UUID" (Full.ImplementsInterfaces []) mempty
+                    $ pure
+                    $ Full.FieldDefinition mempty "value" arguments someType mempty
+                expected = "interface UUID {\n\
+                    \  value(arg: String): String\n\
+                    \}"
+                actual = typeSystemDefinition pretty definition'
+             in actual `shouldBe` expected
+
+        it "encodes an union definition" $
+            let definition' = Full.TypeDefinition
+                    $ Full.UnionTypeDefinition mempty "SearchResult" mempty
+                    $ Full.UnionMemberTypes ["Photo", "Person"]
+                expected = "union SearchResult =\n\
+                    \  | Photo\n\
+                    \  | Person"
+                actual = typeSystemDefinition pretty definition'
+             in actual `shouldBe` expected
+
+        it "encodes an enum definition" $
+            let values =
+                    [ Full.EnumValueDefinition mempty "NORTH" mempty
+                    , Full.EnumValueDefinition mempty "EAST" mempty
+                    , Full.EnumValueDefinition mempty "SOUTH" mempty
+                    , Full.EnumValueDefinition mempty "WEST" mempty
+                    ]
+                definition' = Full.TypeDefinition
+                    $ Full.EnumTypeDefinition mempty "Direction" mempty values
+                expected = "enum Direction {\n\
+                    \  NORTH\n\
+                    \  EAST\n\
+                    \  SOUTH\n\
+                    \  WEST\n\
+                    \}"
+                actual = typeSystemDefinition pretty definition'
+             in actual `shouldBe` expected
+
+        it "encodes an input type" $
+            let intType = Full.TypeNonNull $ Full.NonNullTypeNamed "Int"
+                stringType = Full.TypeNamed "String"
+                fields =
+                    [ Full.InputValueDefinition mempty "a" stringType Nothing mempty
+                    , Full.InputValueDefinition mempty "b" intType Nothing mempty
+                    ]
+                definition' = Full.TypeDefinition
+                    $ Full.InputObjectTypeDefinition mempty "ExampleInputObject" mempty fields
+                expected = "input ExampleInputObject {\n\
+                    \  a: String\n\
+                    \  b: Int!\n\
+                    \}"
+                actual = typeSystemDefinition pretty definition'
+             in actual `shouldBe` expected
+
+        context "directive definition" $ do
+            it "encodes a directive definition" $ do
+                let definition' = Full.DirectiveDefinition mempty "example" mempty False
+                        $ pure
+                        $ DirectiveLocation.ExecutableDirectiveLocation DirectiveLocation.Field
+                    expected = "@example() on\n\
+                        \  | FIELD"
+                    actual = typeSystemDefinition pretty definition'
+                 in actual `shouldBe` expected
+
+            it "encodes a repeatable directive definition" $ do
+                let definition' = Full.DirectiveDefinition mempty "example" mempty True
+                        $ pure
+                        $ DirectiveLocation.ExecutableDirectiveLocation DirectiveLocation.Field
+                    expected = "@example() repeatable on\n\
+                        \  | FIELD"
+                    actual = typeSystemDefinition pretty definition'
+                 in actual `shouldBe` expected

tests/Language/GraphQL/AST/LexerSpec.hs

@@ -0,0 +1,98 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Language.GraphQL.AST.LexerSpec
+    ( spec
+    ) where
+
+import Data.Text (Text)
+import Data.Void (Void)
+import Language.GraphQL.AST.Lexer
+import Test.Hspec (Spec, context, describe, it)
+import Test.Hspec.Megaparsec (shouldParse, shouldFailOn, shouldSucceedOn)
+import Text.Megaparsec (ParseErrorBundle, parse)
+
+spec :: Spec
+spec = describe "Lexer" $ do
+    context "Reference tests" $ do
+        it "accepts BOM header" $
+            parse unicodeBOM "" `shouldSucceedOn` "\xfeff"
+
+        it "lexes strings" $ do
+            parse string "" "\"simple\"" `shouldParse` "simple"
+            parse string "" "\" white space \"" `shouldParse` " white space "
+            parse string "" "\"quote \\\"\"" `shouldParse` "quote \""
+            parse string "" "\"escaped \\n\"" `shouldParse` "escaped \n"
+            parse string "" "\"slashes \\\\ \\/\"" `shouldParse` "slashes \\ /"
+            parse string "" "\"unicode \\u1234\\u5678\\u90AB\\uCDEF\""
+                `shouldParse` "unicode ሴ噸邫췯"
+
+        it "lexes block string" $ do
+            parse blockString "" "\"\"\"simple\"\"\"" `shouldParse` "simple"
+            parse blockString "" "\"\"\" white space \"\"\""
+                `shouldParse` " white space "
+            parse blockString "" "\"\"\"contains \" quote\"\"\""
+                `shouldParse` "contains \" quote"
+            parse blockString "" "\"\"\"contains \\\"\"\" triplequote\"\"\""
+                `shouldParse` "contains \"\"\" triplequote"
+            parse blockString "" "\"\"\"multi\nline\"\"\"" `shouldParse` "multi\nline"
+            parse blockString "" "\"\"\"multi\rline\r\nnormalized\"\"\""
+                `shouldParse` "multi\nline\nnormalized"
+            parse blockString "" "\"\"\"multi\rline\r\nnormalized\"\"\""
+                `shouldParse` "multi\nline\nnormalized"
+            parse blockString "" "\"\"\"unescaped \\n\\r\\b\\t\\f\\u1234\"\"\""
+                `shouldParse` "unescaped \\n\\r\\b\\t\\f\\u1234"
+            parse blockString "" "\"\"\"slashes \\\\ \\/\"\"\""
+                `shouldParse` "slashes \\\\ \\/"
+            parse blockString "" "\"\"\"\n\
+                \\n\
+                \  spans\n\
+                \    multiple\n\
+                \      lines\n\
+                \\n\
+                \\"\"\""
+                `shouldParse` "spans\n  multiple\n    lines"
+
+        it "lexes numbers" $ do
+            parse integer "" "4" `shouldParse` (4 :: Int)
+            parse float "" "4.123" `shouldParse` 4.123
+            parse integer "" "-4" `shouldParse` (-4 :: Int)
+            parse integer "" "9" `shouldParse` (9 :: Int)
+            parse integer "" "0" `shouldParse` (0 :: Int)
+            parse float "" "-4.123" `shouldParse` (-4.123)
+            parse float "" "0.123" `shouldParse` 0.123
+            parse float "" "123e4" `shouldParse` 123e4
+            parse float "" "123E4" `shouldParse` 123E4
+            parse float "" "123e-4" `shouldParse` 123e-4
+            parse float "" "123e+4" `shouldParse` 123e+4
+            parse float "" "-1.123e4" `shouldParse` (-1.123e4)
+            parse float "" "-1.123E4" `shouldParse` (-1.123E4)
+            parse float "" "-1.123e-4" `shouldParse` (-1.123e-4)
+            parse float "" "-1.123e+4" `shouldParse` (-1.123e+4)
+            parse float "" "-1.123e4567" `shouldParse` (-1.123e4567)
+
+        it "lexes punctuation" $ do
+            parse bang "" "!" `shouldParse` "!"
+            parse dollar "" "$" `shouldParse` "$"
+            runBetween parens `shouldSucceedOn` "()"
+            parse spread "" "..." `shouldParse` "..."
+            parse colon "" `shouldSucceedOn` ":"
+            parse equals "" "=" `shouldParse` "="
+            parse at "" `shouldSucceedOn` "@"
+            runBetween brackets `shouldSucceedOn` "[]"
+            runBetween braces `shouldSucceedOn` "{}"
+            parse pipe "" "|" `shouldParse` "|"
+
+    context "Implementation tests" $ do
+        it "lexes empty block strings" $
+            parse blockString "" "\"\"\"\"\"\"" `shouldParse` ""
+        it "lexes ampersand" $
+            parse amp "" "&" `shouldParse` "&"
+        it "lexes schema extensions" $
+            parseExtend "schema" `shouldSucceedOn` "extend schema"
+        it "fails if the given token doesn't match" $
+            parseExtend "schema" `shouldFailOn` "extend shema"
+
+parseExtend :: Text -> (Text -> Either (ParseErrorBundle Text Void) ())
+parseExtend extension = parse (extend extension "" $ pure $ pure ()) ""
+
+runBetween :: (Parser () -> Parser ()) -> Text -> Either (ParseErrorBundle Text Void) ()
+runBetween parser = parse (parser $ pure ()) ""

tests/Language/GraphQL/AST/ParserSpec.hs

@@ -0,0 +1,228 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Language.GraphQL.AST.ParserSpec
+    ( spec
+    ) where
+
+import Data.List.NonEmpty (NonEmpty(..))
+import qualified Data.Text as Text
+import Language.GraphQL.AST.Document
+import qualified Language.GraphQL.AST.DirectiveLocation as DirLoc
+import Language.GraphQL.AST.Parser
+import Test.Hspec (Spec, describe, it, context)
+import Test.Hspec.Megaparsec
+    ( shouldParse
+    , shouldFailOn
+    , parseSatisfies
+    , shouldSucceedOn
+    )
+import Text.Megaparsec (parse)
+import Test.QuickCheck (property, NonEmptyList (..), mapSize)
+import Language.GraphQL.AST.Arbitrary
+
+spec :: Spec
+spec = describe "Parser" $ do
+    it "accepts BOM header" $
+        parse document "" `shouldSucceedOn` "\xfeff{foo}"
+
+    context "Arguments" $ do
+        it "accepts block strings as argument" $
+            parse document "" `shouldSucceedOn`
+                "{ hello(text: \"\"\"Argument\"\"\") }"
+
+        it "accepts strings as argument" $
+            parse document "" `shouldSucceedOn` "{ hello(text: \"Argument\") }"
+
+        it "accepts int as argument" $
+            parse document "" `shouldSucceedOn` "{ user(id: 4) }"
+
+        it "accepts boolean as argument" $
+            parse document "" `shouldSucceedOn`
+                "{ hello(flag: true) { field1 } }"
+
+        it "accepts float as argument" $
+            parse document "" `shouldSucceedOn`
+                "{ body(height: 172.5) { height } }"
+
+        it "accepts empty list as argument" $
+            parse document "" `shouldSucceedOn` "{ query(list: []) { field1 } }"
+
+        it "accepts two required arguments" $
+            parse document "" `shouldSucceedOn`
+                "mutation auth($username: String!, $password: String!) { test }"
+
+        it "accepts two string arguments" $
+            parse document "" `shouldSucceedOn`
+                "mutation auth { test(username: \"username\", password: \"password\") }"
+
+        it "accepts two block string arguments" $
+            let given = "mutation auth {\n\
+                    \  test(username: \"\"\"username\"\"\", password: \"\"\"password\"\"\")\n\
+                    \}"
+             in parse document "" `shouldSucceedOn` given
+
+        it "fails to parse an empty argument list in parens" $
+            parse document "" `shouldFailOn` "{ test() }"
+
+        it "accepts any arguments" $ mapSize (const 10) $ property $ \xs ->
+            let arguments' = map printArgument
+                    $ getNonEmpty (xs :: NonEmptyList (AnyArgument AnyValue))
+                query' = "query(" <> Text.intercalate ", " arguments' <> ")"
+             in parse document "" `shouldSucceedOn` ("{ " <> query' <> " }")
+
+    it "parses minimal schema definition" $
+        parse document "" `shouldSucceedOn` "schema { query: Query }"
+
+    it "parses minimal scalar definition" $
+        parse document "" `shouldSucceedOn` "scalar Time"
+
+    it "parses ImplementsInterfaces" $
+        parse document "" `shouldSucceedOn`
+            "type Person implements NamedEntity & ValuedEntity {\n\
+            \  name: String\n\
+            \}"
+
+    it "parses a  type without ImplementsInterfaces" $
+        parse document "" `shouldSucceedOn`
+            "type Person {\n\
+            \  name: String\n\
+            \}"
+
+    it "parses ArgumentsDefinition in an ObjectDefinition" $
+        parse document "" `shouldSucceedOn`
+            "type Person {\n\
+            \  name(first: String, last: String): String\n\
+            \}"
+
+    it "parses minimal union type definition" $
+        parse document "" `shouldSucceedOn`
+            "union SearchResult = Photo | Person"
+
+    it "parses minimal interface type definition" $
+        parse document "" `shouldSucceedOn`
+            "interface NamedEntity {\n\
+            \  name: String\n\
+            \}"
+
+    it "parses ImplementsInterfaces on interfaces" $
+        parse document "" `shouldSucceedOn`
+            "interface Person implements NamedEntity & ValuedEntity {\n\
+            \  name: String\n\
+            \}"
+
+    it "parses minimal enum type definition" $
+        parse document "" `shouldSucceedOn`
+            "enum Direction {\n\
+            \  NORTH\n\
+            \  EAST\n\
+            \  SOUTH\n\
+            \  WEST\n\
+            \}"
+
+    it "parses minimal input object type definition" $
+        parse document "" `shouldSucceedOn`
+            "input Point2D {\n\
+            \  x: Float\n\
+            \  y: Float\n\
+            \}"
+
+    it "parses minimal input enum definition with an optional pipe" $
+        parse document "" `shouldSucceedOn`
+            "directive @example on\n\
+            \  | FIELD\n\
+            \  | FRAGMENT_SPREAD"
+
+    it "parses two minimal directive definitions" $
+        let directive name' loc = TypeSystemDefinition
+                $ DirectiveDefinition
+                    (Description Nothing)
+                    name'
+                    (ArgumentsDefinition [])
+                    False
+                    (loc :| [])
+            example1 = directive "example1"
+                (DirLoc.TypeSystemDirectiveLocation DirLoc.FieldDefinition)
+                (Location {line = 1, column = 1})
+            example2 = directive "example2"
+                (DirLoc.ExecutableDirectiveLocation DirLoc.Field)
+                (Location {line = 2, column = 1})
+            testSchemaExtension = example1 :| [example2]
+            query = Text.unlines
+                [ "directive @example1 on FIELD_DEFINITION"
+                , "directive @example2 on FIELD"
+                ]
+         in parse document "" query `shouldParse` testSchemaExtension
+
+    it "parses a directive definition with a default empty list argument" $
+        let argumentValue = Just
+                $ Node (ConstList [])
+                $ Location{ line = 1, column = 33 }
+            loc = DirLoc.TypeSystemDirectiveLocation DirLoc.FieldDefinition
+            argumentValueDefinition = InputValueDefinition
+                (Description Nothing)
+                "foo"
+                (TypeList (TypeNamed "String"))
+                argumentValue
+                []
+            definition = DirectiveDefinition
+                (Description Nothing)
+                "test"
+                (ArgumentsDefinition [argumentValueDefinition])
+                False
+                (loc :| [])
+            directive = TypeSystemDefinition definition
+                $ Location{ line = 1, column = 1 }
+            query = "directive @test(foo: [String] = []) on FIELD_DEFINITION"
+         in parse document "" query `shouldParse` (directive :| [])
+
+    it "parses schema extension with a new directive" $
+        parse document "" `shouldSucceedOn` "extend schema @newDirective"
+
+    it "parses schema extension with an operation type definition" $
+        parse document "" `shouldSucceedOn` "extend schema { query: Query }"
+
+    it "parses schema extension with an operation type and directive" $
+        let newDirective = Directive "newDirective" [] $ Location 1 15
+            schemaExtension = SchemaExtension
+                $ SchemaOperationExtension [newDirective]
+                $ OperationTypeDefinition Query "Query" :| []
+            testSchemaExtension = TypeSystemExtension schemaExtension
+                $ Location 1 1
+            query = "extend schema @newDirective { query: Query }"
+         in parse document "" query `shouldParse` (testSchemaExtension :| [])
+
+    it "parses a repeatable directive definition" $
+        let given = "directive @test repeatable on FIELD_DEFINITION"
+            isRepeatable (TypeSystemDefinition definition' _ :| [])
+                | DirectiveDefinition _ _ _ repeatable _ <- definition' = repeatable
+            isRepeatable _ = False
+         in parse document "" given `parseSatisfies` isRepeatable
+
+    it "parses an object extension" $
+        parse document "" `shouldSucceedOn`
+            "extend type Story { isHiddenLocally: Boolean }"
+
+    it "rejects variables in DefaultValue" $
+        parse document "" `shouldFailOn`
+            "query ($book: String = \"Zarathustra\", $author: String = $book) {\n\
+            \  title\n\
+            \}"
+
+    it "rejects empty selection set" $
+       parse document "" `shouldFailOn` "query { innerField {} }"
+
+    it "parses documents beginning with a comment" $
+        parse document "" `shouldSucceedOn`
+            "\"\"\"\n\
+            \Query\n\
+            \\"\"\"\n\
+            \type Query {\n\
+            \  queryField: String\n\
+            \}"
+
+    it "parses subscriptions" $
+        parse document "" `shouldSucceedOn`
+            "subscription NewMessages {\n\
+            \  newMessage(roomId: 123) {\n\
+            \    sender\n\
+            \  }\n\
+            \}"

tests/Language/GraphQL/ErrorSpec.hs

@@ -0,0 +1,36 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE OverloadedStrings #-}
+module Language.GraphQL.ErrorSpec
+    ( spec
+    ) where
+
+import Data.List.NonEmpty (NonEmpty (..))
+import Language.GraphQL.Error
+import qualified Language.GraphQL.Type as Type
+import Test.Hspec
+    ( Spec
+    , describe
+    , it
+    , shouldBe
+    )
+import Text.Megaparsec (PosState(..))
+import Text.Megaparsec.Error (ParseError(..), ParseErrorBundle(..))
+import Text.Megaparsec.Pos (SourcePos(..), mkPos)
+
+spec :: Spec
+spec = describe "parseError" $
+    it "generates response with a single error" $ do
+        let parseErrors = TrivialError 0 Nothing mempty :| []
+            posState = PosState
+                { pstateInput = ""
+                , pstateOffset = 0
+                , pstateSourcePos = SourcePos "" (mkPos 1) (mkPos 1)
+                , pstateTabWidth = mkPos 1
+                , pstateLinePrefix = ""
+                }
+        Response Type.Null actual <-
+            parseError (ParseErrorBundle parseErrors posState)
+        length actual `shouldBe` 1

tests/Language/GraphQL/Execute/CoerceSpec.hs

@@ -0,0 +1,52 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE OverloadedStrings #-}
+module Language.GraphQL.Execute.CoerceSpec
+    ( spec
+    ) where
+
+import qualified Data.HashMap.Strict as HashMap
+import Data.Maybe (isNothing)
+import qualified Language.GraphQL.Execute.Coerce as Coerce
+import Language.GraphQL.Type
+import qualified Language.GraphQL.Type.In as In
+import Prelude hiding (id)
+import Test.Hspec (Spec, describe, it, shouldBe, shouldSatisfy)
+
+direction :: EnumType
+direction = EnumType "Direction" Nothing  $ HashMap.fromList
+    [ ("NORTH", EnumValue Nothing)
+    , ("EAST", EnumValue Nothing)
+    , ("SOUTH", EnumValue Nothing)
+    , ("WEST", EnumValue Nothing)
+    ]
+
+namedIdType :: In.Type
+namedIdType = In.NamedScalarType id
+
+spec :: Spec
+spec =
+    describe "coerceInputLiteral" $ do
+        it "coerces enums" $
+            let expected = Just (Enum "NORTH")
+                actual = Coerce.coerceInputLiteral
+                    (In.NamedEnumType direction) (Enum "NORTH")
+             in actual `shouldBe` expected
+        it "fails with non-existing enum value" $
+            let actual = Coerce.coerceInputLiteral
+                    (In.NamedEnumType direction) (Enum "NORTH_EAST")
+             in actual `shouldSatisfy` isNothing
+        it "coerces integers to IDs" $
+            let expected = Just (String "1234")
+                actual = Coerce.coerceInputLiteral namedIdType (Int 1234)
+             in actual `shouldBe` expected
+        it "coerces nulls" $ do
+            let actual = Coerce.coerceInputLiteral namedIdType Null
+             in actual `shouldBe` Just Null
+        it "wraps singleton lists" $ do
+            let expected = Just $ List [List [String "1"]]
+                embeddedType = In.ListType $ In.ListType namedIdType
+                actual = Coerce.coerceInputLiteral embeddedType (String "1")
+             in actual `shouldBe` expected

tests/Language/GraphQL/Execute/OrderedMapSpec.hs

@@ -0,0 +1,72 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE OverloadedStrings #-}
+
+module Language.GraphQL.Execute.OrderedMapSpec
+    ( spec
+    ) where
+
+import Language.GraphQL.Execute.OrderedMap (OrderedMap)
+import qualified Language.GraphQL.Execute.OrderedMap as OrderedMap
+import Test.Hspec (Spec, describe, it, shouldBe, shouldSatisfy)
+
+spec :: Spec
+spec =
+    describe "OrderedMap" $ do
+        it "creates an empty map" $
+            (mempty :: OrderedMap String) `shouldSatisfy` null
+
+        it "creates a singleton" $
+            let value :: String
+                value = "value"
+             in OrderedMap.size (OrderedMap.singleton "key" value) `shouldBe` 1
+
+        it "combines inserted vales" $
+            let key = "key"
+                map1 = OrderedMap.singleton key ("1" :: String)
+                map2 = OrderedMap.singleton key ("2" :: String)
+             in OrderedMap.lookup key (map1 <> map2) `shouldBe` Just "12"
+
+        it "shows the map" $
+            let actual = show
+                    $ OrderedMap.insert "key1" "1"
+                    $ OrderedMap.singleton "key2" ("2" :: String)
+                expected = "fromList [(\"key2\",\"2\"),(\"key1\",\"1\")]"
+             in actual `shouldBe` expected
+
+        it "traverses a map of just values" $
+            let actual = sequence
+                    $ OrderedMap.insert "key1" (Just "2")
+                    $ OrderedMap.singleton "key2" $ Just ("1" :: String)
+                expected = Just
+                    $ OrderedMap.insert "key1" "2"
+                    $ OrderedMap.singleton "key2" ("1" :: String)
+             in actual `shouldBe` expected
+
+        it "traverses a map with a Nothing" $
+            let actual = sequence
+                    $ OrderedMap.insert "key1" Nothing
+                    $ OrderedMap.singleton "key2" $ Just ("1" :: String)
+                expected = Nothing
+             in actual `shouldBe` expected
+
+        it "combines two maps preserving the order of the second one" $
+            let map1 :: OrderedMap String
+                map1 = OrderedMap.insert "key2" "2"
+                    $ OrderedMap.singleton "key1" "1"
+                map2 :: OrderedMap String
+                map2 = OrderedMap.insert "key4" "4"
+                    $ OrderedMap.singleton "key3" "3"
+                expected = OrderedMap.insert "key4" "4"
+                    $ OrderedMap.insert "key3" "3"
+                    $ OrderedMap.insert "key2" "2"
+                    $ OrderedMap.singleton "key1" "1"
+             in (map1 <> map2) `shouldBe` expected
+
+        it "replaces existing values" $
+            let key = "key"
+                actual = OrderedMap.replace key ("2" :: String)
+                        $ OrderedMap.singleton key ("1" :: String)
+             in OrderedMap.lookup key actual `shouldBe` Just "2"

tests/Language/GraphQL/ExecuteSpec.hs

@@ -0,0 +1,470 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+module Language.GraphQL.ExecuteSpec
+    ( spec
+    ) where
+
+import Control.Exception (Exception(..))
+import Control.Monad.Catch (throwM)
+import Data.Conduit
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as HashMap
+import Data.Typeable (cast)
+import Language.GraphQL.AST (Document, Location(..), Name)
+import Language.GraphQL.AST.Parser (document)
+import Language.GraphQL.Error
+import Language.GraphQL.Execute (execute)
+import qualified Language.GraphQL.Type.Schema as Schema
+import qualified Language.GraphQL.Type as Type
+import Language.GraphQL.Type
+import qualified Language.GraphQL.Type.In as In
+import qualified Language.GraphQL.Type.Out as Out
+import Prelude hiding (id)
+import Test.Hspec (Spec, context, describe, it, shouldBe)
+import Text.Megaparsec (parse, errorBundlePretty)
+import Schemas.HeroSchema (heroSchema)
+import Data.Maybe (fromJust)
+import qualified Data.Sequence as Seq
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Test.Hspec.Expectations
+    ( Expectation
+    , expectationFailure
+    )
+import Data.Either (fromRight)
+
+data PhilosopherException = PhilosopherException
+    deriving Show
+
+instance Exception PhilosopherException where
+    toException = toException. ResolverException
+    fromException e = do
+        ResolverException resolverException <- fromException e
+        cast resolverException
+
+philosopherSchema :: Schema IO
+philosopherSchema =
+    schemaWithTypes Nothing queryType Nothing subscriptionRoot extraTypes mempty
+  where
+    subscriptionRoot = Just subscriptionType
+    extraTypes =
+        [ Schema.ObjectType bookType
+        , Schema.ObjectType bookCollectionType
+        ]
+
+queryType :: Out.ObjectType IO
+queryType = Out.ObjectType "Query" Nothing []
+    $ HashMap.fromList
+    [ ("philosopher", ValueResolver philosopherField philosopherResolver)
+    , ("throwing", ValueResolver throwingField throwingResolver)
+    , ("count", ValueResolver countField countResolver)
+    , ("sequence", ValueResolver sequenceField sequenceResolver)
+    , ("withInputObject", ValueResolver withInputObjectField withInputObjectResolver)
+    ]
+  where
+    philosopherField =
+        Out.Field Nothing (Out.NamedObjectType philosopherType)
+        $ HashMap.singleton "id"
+        $ In.Argument Nothing (In.NamedScalarType id) Nothing
+    philosopherResolver = pure $ Object mempty
+    throwingField =
+        let fieldType = Out.ListType $ Out.NonNullScalarType string
+         in Out.Field Nothing fieldType HashMap.empty
+    throwingResolver :: Resolve IO
+    throwingResolver = throwM PhilosopherException
+    countField =
+        let fieldType = Out.NonNullScalarType int
+         in Out.Field Nothing fieldType HashMap.empty
+    countResolver = pure ""
+    sequenceField =
+        let fieldType = Out.ListType $ Out.NonNullScalarType int
+         in Out.Field Nothing fieldType HashMap.empty
+    sequenceResolver = pure intSequence
+    withInputObjectResolver = pure $ Type.Int 0
+    withInputObjectField =
+        Out.Field Nothing (Out.NonNullScalarType int) $ HashMap.fromList
+            [("values", In.Argument Nothing withInputObjectArgumentType Nothing)]
+    withInputObjectArgumentType = In.NonNullListType
+        $ In.NonNullInputObjectType inputObjectType
+
+inputObjectType :: In.InputObjectType
+inputObjectType = In.InputObjectType "InputObject" Nothing $
+    HashMap.singleton "name" $
+        In.InputField Nothing (In.NonNullScalarType int) Nothing
+
+intSequence :: Value
+intSequence = Type.List [Type.Int 1, Type.Int 2, Type.Int 3]
+
+musicType :: Out.ObjectType IO
+musicType = Out.ObjectType "Music" Nothing []
+    $ HashMap.fromList resolvers
+  where
+    resolvers =
+        [ ("instrument", ValueResolver instrumentField instrumentResolver)
+        ]
+    instrumentResolver = pure $ String "piano"
+    instrumentField = Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
+
+poetryType :: Out.ObjectType IO
+poetryType = Out.ObjectType "Poetry" Nothing []
+    $ HashMap.fromList resolvers
+  where
+    resolvers =
+        [ ("genre", ValueResolver genreField genreResolver)
+        ]
+    genreResolver = pure $ String "Futurism"
+    genreField = Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
+
+interestType :: Out.UnionType IO
+interestType = Out.UnionType "Interest" Nothing [musicType, poetryType]
+
+philosopherType :: Out.ObjectType IO
+philosopherType = Out.ObjectType "Philosopher" Nothing []
+    $ HashMap.fromList resolvers
+  where
+    resolvers =
+        [ ("firstName", ValueResolver firstNameField firstNameResolver)
+        , ("lastName", ValueResolver lastNameField lastNameResolver)
+        , ("school", ValueResolver schoolField schoolResolver)
+        , ("interest", ValueResolver interestField interestResolver)
+        , ("majorWork", ValueResolver majorWorkField majorWorkResolver)
+        , ("century", ValueResolver centuryField centuryResolver)
+        , ("firstLanguage", ValueResolver firstLanguageField firstLanguageResolver)
+        ]
+    firstNameField =
+        Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
+    firstNameResolver = pure $ String "Friedrich"
+    lastNameField
+        = Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
+    lastNameResolver = pure $ String "Nietzsche"
+    schoolField
+       = Out.Field Nothing (Out.NonNullEnumType schoolType) HashMap.empty
+    schoolResolver = pure $ Enum "EXISTENTIALISM"
+    interestField
+        = Out.Field Nothing (Out.NonNullUnionType interestType) HashMap.empty
+    interestResolver = pure
+        $ Object
+        $ HashMap.fromList [("instrument", "piano")]
+    majorWorkField
+        = Out.Field Nothing (Out.NonNullInterfaceType workType) HashMap.empty
+    majorWorkResolver = pure
+        $ Object
+        $ HashMap.fromList
+            [ ("title", "Also sprach Zarathustra: Ein Buch für Alle und Keinen")
+            ]
+    centuryField =
+        Out.Field Nothing (Out.NonNullScalarType int) HashMap.empty
+    centuryResolver = pure $ Float 18.5
+    firstLanguageField
+        = Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
+    firstLanguageResolver = pure Null
+
+workType :: Out.InterfaceType IO
+workType = Out.InterfaceType "Work" Nothing []
+    $ HashMap.fromList fields
+  where
+    fields = [("title", titleField)]
+    titleField = Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
+
+bookType :: Out.ObjectType IO
+bookType = Out.ObjectType "Book" Nothing [workType]
+    $ HashMap.fromList resolvers
+  where
+    resolvers =
+        [ ("title", ValueResolver titleField titleResolver)
+        ]
+    titleField = Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
+    titleResolver = pure "Also sprach Zarathustra: Ein Buch für Alle und Keinen"
+
+bookCollectionType :: Out.ObjectType IO
+bookCollectionType = Out.ObjectType "Book" Nothing [workType]
+    $ HashMap.fromList resolvers
+  where
+    resolvers =
+        [ ("title", ValueResolver titleField titleResolver)
+        ]
+    titleField = Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
+    titleResolver = pure "The Three Critiques"
+
+subscriptionType :: Out.ObjectType IO
+subscriptionType = Out.ObjectType "Subscription" Nothing []
+    $ HashMap.singleton "newQuote"
+    $ EventStreamResolver quoteField (pure $ Object mempty)
+    $ pure $ yield $ Object mempty
+  where
+    quoteField =
+        Out.Field Nothing (Out.NonNullObjectType quoteType) HashMap.empty
+
+quoteType :: Out.ObjectType IO
+quoteType = Out.ObjectType "Quote" Nothing []
+    $ HashMap.singleton "quote"
+    $ ValueResolver quoteField
+    $ pure "Naturam expelles furca, tamen usque recurret."
+  where
+    quoteField =
+        Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
+
+schoolType :: Type.EnumType
+schoolType = EnumType "School" Nothing $ HashMap.fromList
+    [ ("NOMINALISM", EnumValue Nothing)
+    , ("REALISM", EnumValue Nothing)
+    , ("IDEALISM", EnumValue Nothing)
+    ]
+
+type EitherStreamOrValue = Either
+    (ResponseEventStream IO Type.Value)
+    (Response Type.Value)
+
+-- Asserts that a query resolves to a value.
+shouldResolveTo :: Text.Text -> Response Type.Value -> Expectation
+shouldResolveTo querySource expected =
+    case parse document "" querySource of
+        (Right parsedDocument) ->
+            execute philosopherSchema Nothing (mempty :: HashMap Name Type.Value) parsedDocument >>= go
+        (Left errorBundle) -> expectationFailure $ errorBundlePretty errorBundle
+  where
+    go = \case
+        Right result -> shouldBe result expected
+        Left _ -> expectationFailure
+            "the query is expected to resolve to a value, but it resolved to an event stream"
+
+-- Asserts that the executor produces an error that starts with a string.
+shouldContainError :: Either (ResponseEventStream IO Type.Value) (Response Type.Value)
+    -> Text
+    -> Expectation
+shouldContainError streamOrValue expected =
+    case streamOrValue of
+        Right response -> respond response
+        Left _ -> expectationFailure
+            "the query is expected to resolve to a value, but it resolved to an event stream"
+  where
+    startsWith :: Text.Text -> Text.Text -> Bool
+    startsWith xs ys = Text.take (Text.length ys) xs == ys
+    respond :: Response Type.Value -> Expectation
+    respond Response{ errors }
+        | any ((`startsWith` expected) . message) errors = pure ()
+        | otherwise = expectationFailure
+            "the query is expected to execute with errors, but the response doesn't contain any errors"
+
+parseAndExecute :: Schema IO
+    -> Maybe Text
+    -> HashMap Name Type.Value
+    -> Text
+    -> IO (Either (ResponseEventStream IO Type.Value) (Response Type.Value))
+parseAndExecute schema' operation variables
+    = either (pure . parseError) (execute schema' operation variables)
+    . parse document ""
+
+spec :: Spec
+spec =
+    describe "execute" $ do
+        it "rejects recursive fragments" $
+            let sourceQuery = "\
+              \{\n\
+              \  ...cyclicFragment\n\
+              \}\n\
+              \\n\
+              \fragment cyclicFragment on Query {\n\
+              \  ...cyclicFragment\n\
+              \}\
+              \"
+                expected = Response (Object mempty) mempty
+             in sourceQuery `shouldResolveTo` expected
+
+        context "Query" $ do
+            it "skips unknown fields" $
+                let data'' = Object
+                        $ HashMap.singleton "philosopher"
+                        $ Object
+                        $ HashMap.singleton "firstName"
+                        $ String "Friedrich"
+                    expected = Response data'' mempty
+                    sourceQuery = "{ philosopher { firstName surname } }"
+                in sourceQuery `shouldResolveTo` expected
+            it "merges selections" $
+                let data'' = Object
+                        $ HashMap.singleton "philosopher"
+                        $ Object
+                        $ HashMap.fromList
+                            [ ("firstName", String "Friedrich")
+                            , ("lastName", String "Nietzsche")
+                            ]
+                    expected = Response data'' mempty
+                    sourceQuery = "{ philosopher { firstName } philosopher { lastName } }"
+                in sourceQuery `shouldResolveTo` expected
+
+            it "errors on invalid output enum values" $
+                let data'' = Object $ HashMap.singleton "philosopher" Null
+                    executionErrors = pure $ Error
+                        { message =
+                            "Value completion error. Expected type School!, found: EXISTENTIALISM."
+                        , locations = [Location 1 17]
+                        , path = [Segment "philosopher", Segment "school"]
+                        }
+                    expected = Response data'' executionErrors
+                    sourceQuery = "{ philosopher { school } }"
+                 in sourceQuery `shouldResolveTo` expected
+
+            it "gives location information for non-null unions" $
+                let data'' = Object $ HashMap.singleton "philosopher" Null
+                    executionErrors = pure $ Error
+                        { message =
+                            "Value completion error. Expected type Interest!, found: { instrument: \"piano\" }."
+                        , locations = [Location 1 17]
+                        , path = [Segment "philosopher", Segment "interest"]
+                        }
+                    expected = Response data'' executionErrors
+                    sourceQuery = "{ philosopher { interest } }"
+                 in sourceQuery `shouldResolveTo` expected
+
+            it "gives location information for invalid interfaces" $
+                let data'' = Object $ HashMap.singleton "philosopher" Null
+                    executionErrors = pure $ Error
+                        { message
+                            = "Value completion error. Expected type Work!, found:\
+                            \ { title: \"Also sprach Zarathustra: Ein Buch f\252r Alle und Keinen\" }."
+                        , locations = [Location 1 17]
+                        , path = [Segment "philosopher", Segment "majorWork"]
+                        }
+                    expected = Response data'' executionErrors
+                    sourceQuery = "{ philosopher { majorWork { title } } }"
+                 in sourceQuery `shouldResolveTo` expected
+
+            it "gives location information for failed result coercion" $
+                let data'' = Object $ HashMap.singleton "philosopher" Null
+                    executionErrors = pure $ Error
+                        { message = "Unable to coerce result to Int!."
+                        , locations = [Location 1 26]
+                        , path = [Segment "philosopher", Segment "century"]
+                        }
+                    expected = Response data'' executionErrors
+                    sourceQuery = "{ philosopher(id: \"1\") { century } }"
+                in sourceQuery `shouldResolveTo` expected
+
+            it "gives location information for failed result coercion" $
+                let data'' = Object $ HashMap.singleton "throwing" Null
+                    executionErrors = pure $ Error
+                        { message = "PhilosopherException"
+                        , locations = [Location 1 3]
+                        , path = [Segment "throwing"]
+                        }
+                    expected = Response data'' executionErrors
+                    sourceQuery = "{ throwing }"
+                in sourceQuery `shouldResolveTo` expected
+
+            it "sets data to null if a root field isn't nullable" $
+                let executionErrors = pure $ Error
+                        { message = "Unable to coerce result to Int!."
+                        , locations = [Location 1 3]
+                        , path = [Segment "count"]
+                        }
+                    expected = Response Null executionErrors
+                    sourceQuery = "{ count }"
+                in sourceQuery `shouldResolveTo` expected
+
+            it "detects nullability errors" $
+                let data'' = Object $ HashMap.singleton "philosopher" Null
+                    executionErrors = pure $ Error
+                        { message = "Value completion error. Expected type String!, found: null."
+                        , locations = [Location 1 26]
+                        , path = [Segment "philosopher", Segment "firstLanguage"]
+                        }
+                    expected = Response data'' executionErrors
+                    sourceQuery = "{ philosopher(id: \"1\") { firstLanguage } }"
+                in sourceQuery `shouldResolveTo` expected
+
+            it "returns list elements in the original order" $
+                let data'' = Object $ HashMap.singleton "sequence" intSequence
+                    expected = Response data'' mempty
+                    sourceQuery = "{ sequence }"
+                in sourceQuery `shouldResolveTo` expected
+
+            context "Arguments" $ do
+                it "gives location information for invalid scalar arguments" $
+                    let data'' = Object $ HashMap.singleton "philosopher" Null
+                        executionErrors = pure $ Error
+                            { message =
+                                "Argument \"id\" has invalid type. Expected type ID, found: True."
+                            , locations = [Location 1 15]
+                            , path = [Segment "philosopher"]
+                            }
+                        expected = Response data'' executionErrors
+                        sourceQuery = "{ philosopher(id: true) { lastName } }"
+                    in sourceQuery `shouldResolveTo` expected
+
+                it "puts an object in a list if needed" $
+                    let data'' = Object $ HashMap.singleton "withInputObject" $ Type.Int 0
+                        expected = Response data'' mempty
+                        sourceQuery = "{ withInputObject(values: { name: 0 }) }"
+                    in sourceQuery `shouldResolveTo` expected
+
+            context "queryError" $ do
+                let namedQuery name = "query " <> name <> " { philosopher(id: \"1\") { interest } }"
+                    twoQueries = namedQuery "A" <> " " <> namedQuery "B"
+
+                it "throws operation name is required error" $ do
+                    let expectedErrorMessage = "Operation name is required"
+                    actual <- parseAndExecute philosopherSchema Nothing mempty twoQueries
+                    actual `shouldContainError` expectedErrorMessage
+
+                it "throws operation not found error" $ do
+                    let expectedErrorMessage = "Operation \"C\" is not found"
+                    actual <- parseAndExecute philosopherSchema (Just "C") mempty twoQueries
+                    actual `shouldContainError` expectedErrorMessage
+
+                it "throws variable coercion error" $ do
+                    let data'' = Null
+                        executionErrors = pure $ Error
+                            { message = "Failed to coerce the variable $id: String."
+                            , locations =[Location 1 7]
+                            , path = []
+                            }
+                        expected = Response data'' executionErrors
+                        executeWithVars = execute philosopherSchema Nothing (HashMap.singleton "id" (Type.Int 1))
+                    Right actual <- either (pure . parseError) executeWithVars
+                        $ parse document "" "query($id: String) { philosopher(id: \"1\") { firstLanguage } }"
+                    actual `shouldBe` expected
+
+                it "throws variable unkown input type error" $
+                    let data'' = Null
+                        executionErrors = pure $ Error
+                            { message = "Variable $id has unknown type Cat."
+                            , locations =[Location 1 7]
+                            , path = []
+                            }
+                        expected = Response data'' executionErrors
+                        sourceQuery = "query($id: Cat) { philosopher(id: \"1\") { firstLanguage } }"
+                     in sourceQuery `shouldResolveTo` expected
+
+            context "Error path" $ do
+                let executeHero :: Document -> IO EitherStreamOrValue
+                    executeHero = execute heroSchema Nothing (HashMap.empty :: HashMap Name Type.Value)
+
+                it "at the beggining of the list" $ do
+                    Right actual <- either (pure . parseError) executeHero
+                        $ parse document "" "{ hero(id: \"1\") { friends { name } } }"
+                    let Response _ errors' = actual
+                        Error _ _ path' = fromJust $ Seq.lookup 0 errors'
+                        expected = [Segment "hero", Segment "friends", Index 0, Segment "name"]
+                     in path' `shouldBe` expected
+
+        context "Subscription" $
+            it "subscribes" $ do
+                let data'' = Object
+                        $ HashMap.singleton "newQuote"
+                        $ Object
+                        $ HashMap.singleton "quote"
+                        $ String "Naturam expelles furca, tamen usque recurret."
+                    expected = Response data'' mempty
+                Left stream <- execute philosopherSchema Nothing (mempty :: HashMap Name Type.Value)
+                    $ fromRight (error "Parse error")
+                    $ parse document "" "subscription { newQuote { quote } }"
+                Just actual <- runConduit $ stream .| await
+                actual `shouldBe` expected

tests/Language/GraphQL/Type/OutSpec.hs

@@ -0,0 +1,18 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE OverloadedStrings #-}
+module Language.GraphQL.Type.OutSpec
+    ( spec
+    ) where
+
+import Language.GraphQL.Type
+import Test.Hspec (Spec, describe, it, shouldBe)
+
+spec :: Spec
+spec =
+    describe "Value" $
+        it "supports overloaded strings" $
+            let nietzsche = "Goldstaub abblasen." :: Value
+             in nietzsche `shouldBe` String "Goldstaub abblasen."

tests/Language/GraphQL/Validate/RulesSpec.hs

@@ -0,0 +1,938 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE OverloadedStrings #-}
+
+module Language.GraphQL.Validate.RulesSpec
+    ( spec
+    ) where
+
+import Data.Foldable (toList)
+import qualified Data.HashMap.Strict as HashMap
+import Data.Text (Text)
+import qualified Language.GraphQL.AST as AST
+import Language.GraphQL.Type
+import qualified Language.GraphQL.Type.Schema as Schema
+import qualified Language.GraphQL.AST.DirectiveLocation as DirectiveLocation
+import qualified Language.GraphQL.Type.In as In
+import qualified Language.GraphQL.Type.Out as Out
+import Language.GraphQL.Validate
+import Test.Hspec (Spec, context, describe, it, shouldBe, shouldContain, xit)
+import Text.Megaparsec (parse, errorBundlePretty)
+
+petSchema :: Schema IO
+petSchema = schema queryType Nothing (Just subscriptionType)
+    $ HashMap.singleton "repeat"
+    $ Schema.Directive Nothing mempty True [DirectiveLocation.ExecutableDirectiveLocation DirectiveLocation.Field]
+
+queryType :: ObjectType IO
+queryType = ObjectType "Query" Nothing [] $ HashMap.fromList
+    [ ("dog", dogResolver)
+    , ("cat", catResolver)
+    , ("findDog", findDogResolver)
+    , ("findCats", findCatsResolver)
+    ]
+  where
+    dogField = Field Nothing (Out.NamedObjectType dogType) mempty
+    dogResolver = ValueResolver dogField $ pure Null
+    findDogArguments = HashMap.singleton "complex"
+        $ In.Argument Nothing (In.NonNullInputObjectType dogDataType) Nothing
+    findDogField = Field Nothing (Out.NamedObjectType dogType) findDogArguments
+    findDogResolver = ValueResolver findDogField $ pure Null
+    catField = Field Nothing (Out.NamedObjectType catType) mempty
+    catResolver = ValueResolver catField $ pure Null
+    findCatsArguments = HashMap.singleton "commands"
+        $ In.Argument Nothing (In.NonNullListType $ In.NonNullEnumType catCommandType)
+        $ Just $ List []
+    findCatsField = Field Nothing (Out.NonNullListType $ Out.NonNullObjectType catType) findCatsArguments
+    findCatsResolver = ValueResolver findCatsField $ pure $ List []
+
+catCommandType :: EnumType
+catCommandType = EnumType "CatCommand" Nothing $ HashMap.fromList
+    [ ("JUMP", EnumValue Nothing)
+    ]
+
+catType :: ObjectType IO
+catType = ObjectType "Cat" Nothing [petType] $ HashMap.fromList
+    [ ("name", nameResolver)
+    , ("nickname", nicknameResolver)
+    , ("doesKnowCommands", doesKnowCommandsResolver)
+    , ("meowVolume", meowVolumeResolver)
+    ]
+  where
+    meowVolumeField = Field Nothing (Out.NamedScalarType int) mempty
+    meowVolumeResolver = ValueResolver meowVolumeField $ pure $ Int 3
+    doesKnowCommandsType = In.NonNullListType
+        $ In.NonNullEnumType catCommandType
+    doesKnowCommandsField = Field Nothing (Out.NonNullScalarType boolean)
+        $ HashMap.singleton "catCommands"
+        $ In.Argument Nothing doesKnowCommandsType Nothing
+    doesKnowCommandsResolver = ValueResolver doesKnowCommandsField
+        $ pure $ Boolean True
+
+nameResolver :: Resolver IO
+nameResolver = ValueResolver nameField $ pure "Name"
+  where
+    nameField = Field Nothing (Out.NonNullScalarType string) mempty
+
+nicknameResolver :: Resolver IO
+nicknameResolver = ValueResolver nicknameField $ pure "Nickname"
+  where
+    nicknameField = Field Nothing (Out.NamedScalarType string) mempty
+
+dogCommandType :: EnumType
+dogCommandType = EnumType "DogCommand" Nothing $ HashMap.fromList
+    [ ("SIT", EnumValue Nothing)
+    , ("DOWN", EnumValue Nothing)
+    , ("HEEL", EnumValue Nothing)
+    ]
+
+dogType :: ObjectType IO
+dogType = ObjectType "Dog" Nothing [petType] $ HashMap.fromList
+    [ ("name", nameResolver)
+    , ("nickname", nicknameResolver)
+    , ("barkVolume", barkVolumeResolver)
+    , ("doesKnowCommand", doesKnowCommandResolver)
+    , ("isHouseTrained", isHouseTrainedResolver)
+    , ("owner", ownerResolver)
+    ]
+  where
+    barkVolumeField = Field Nothing (Out.NamedScalarType int) mempty
+    barkVolumeResolver = ValueResolver barkVolumeField $ pure $ Int 3
+    doesKnowCommandField = Field Nothing (Out.NonNullScalarType boolean)
+        $ HashMap.singleton "dogCommand"
+        $ In.Argument Nothing (In.NonNullEnumType dogCommandType) Nothing
+    doesKnowCommandResolver = ValueResolver doesKnowCommandField
+        $ pure $ Boolean True
+    isHouseTrainedField = Field Nothing (Out.NonNullScalarType boolean)
+        $ HashMap.singleton "atOtherHomes"
+        $ In.Argument Nothing (In.NamedScalarType boolean) Nothing
+    isHouseTrainedResolver = ValueResolver isHouseTrainedField
+        $ pure $ Boolean True
+    ownerField = Field Nothing (Out.NamedObjectType humanType) mempty
+    ownerResolver = ValueResolver ownerField $ pure Null
+
+dogDataType :: InputObjectType
+dogDataType = InputObjectType "DogData" Nothing
+    $ HashMap.singleton "name" nameInputField
+  where
+    nameInputField = InputField Nothing (In.NonNullScalarType string) Nothing
+
+sentientType :: InterfaceType IO
+sentientType = InterfaceType "Sentient" Nothing []
+    $ HashMap.singleton "name"
+    $ Field Nothing (Out.NonNullScalarType string) mempty
+
+petType :: InterfaceType IO
+petType = InterfaceType "Pet" Nothing []
+    $ HashMap.singleton "name"
+    $ Field Nothing (Out.NonNullScalarType string) mempty
+
+subscriptionType :: ObjectType IO
+subscriptionType = ObjectType "Subscription" Nothing [] $ HashMap.fromList
+    [ ("newMessage", newMessageResolver)
+    , ("disallowedSecondRootField", newMessageResolver)
+    ]
+  where
+    newMessageField = Field Nothing (Out.NonNullObjectType messageType) mempty
+    newMessageResolver = ValueResolver newMessageField
+        $ pure $ Object HashMap.empty
+
+messageType :: ObjectType IO
+messageType = ObjectType "Message" Nothing [] $ HashMap.fromList
+    [ ("sender", senderResolver)
+    , ("body", bodyResolver)
+    ]
+  where
+    senderField = Field Nothing (Out.NonNullScalarType string) mempty
+    senderResolver = ValueResolver senderField $ pure "Sender"
+    bodyField = Field Nothing (Out.NonNullScalarType string) mempty
+    bodyResolver = ValueResolver bodyField $ pure "Message body."
+
+humanType :: ObjectType IO
+humanType = ObjectType "Human" Nothing [sentientType] $ HashMap.fromList
+    [ ("name", nameResolver)
+    , ("pets", petsResolver)
+    ]
+  where
+    petsField =
+        Field Nothing (Out.ListType $ Out.NonNullInterfaceType petType) mempty
+    petsResolver = ValueResolver petsField $ pure $ List []
+
+validate :: Text -> [Error]
+validate queryString =
+    case parse AST.document "" queryString of
+        Left parseErrors -> error $ errorBundlePretty parseErrors
+        Right ast -> toList $ document petSchema specifiedRules ast
+
+spec :: Spec
+spec =
+    describe "document" $ do
+        context "executableDefinitionsRule" $
+            it "rejects type definitions" $
+                let queryString = "query getDogName {\n\
+                        \  dog {\n\
+                        \    name\n\
+                        \    color\n\
+                        \  }\n\
+                        \}\n\
+                        \\n\
+                        \extend type Dog {\n\
+                        \  color: String\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Definition must be OperationDefinition or \
+                            \FragmentDefinition."
+                        , locations = [AST.Location 8 1]
+                        }
+                 in validate queryString `shouldContain` [expected]
+
+        context "singleFieldSubscriptionsRule" $ do
+            it "rejects multiple subscription root fields" $
+                let queryString = "subscription sub {\n\
+                        \  newMessage {\n\
+                        \    body\n\
+                        \    sender\n\
+                        \  }\n\
+                        \  disallowedSecondRootField\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Subscription \"sub\" must select only one top \
+                            \level field."
+                        , locations = [AST.Location 1 1]
+                        }
+                 in validate queryString `shouldContain` [expected]
+
+            xit "rejects an introspection field as the subscription root" $
+                let queryString = "subscription sub {\n\
+                        \  __typename\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Subscription \"sub\" must select only one top \
+                            \level field."
+                        , locations = [AST.Location 1 1]
+                        }
+                 in validate queryString `shouldContain` [expected]
+
+            it "rejects multiple subscription root fields coming from a fragment" $
+                let queryString = "subscription sub {\n\
+                        \  ...multipleSubscriptions\n\
+                        \}\n\
+                        \\n\
+                        \fragment multipleSubscriptions on Subscription {\n\
+                        \  newMessage {\n\
+                        \    body\n\
+                        \    sender\n\
+                        \  }\n\
+                        \  disallowedSecondRootField\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Subscription \"sub\" must select only one top \
+                            \level field."
+                        , locations = [AST.Location 1 1]
+                        }
+                 in validate queryString `shouldContain` [expected]
+
+            it "finds corresponding subscription fragment" $
+                let queryString = "subscription sub {\n\
+                        \  ...anotherSubscription\n\
+                        \  ...multipleSubscriptions\n\
+                        \}\n\
+                        \fragment multipleSubscriptions on Subscription {\n\
+                        \  newMessage {\n\
+                        \    body\n\
+                        \  }\n\
+                        \  disallowedSecondRootField {\n\
+                        \    sender\n\
+                        \  }\n\
+                        \}\n\
+                        \fragment anotherSubscription on Subscription {\n\
+                        \  newMessage {\n\
+                        \    body\n\
+                        \    sender\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Subscription \"sub\" must select only one top \
+                            \level field."
+                        , locations = [AST.Location 1 1]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "loneAnonymousOperationRule" $
+            it "rejects multiple anonymous operations" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}\n\
+                        \\n\
+                        \query getName {\n\
+                        \  dog {\n\
+                        \    owner {\n\
+                        \      name\n\
+                        \    }\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "This anonymous operation must be the only defined \
+                            \operation."
+                        , locations = [AST.Location 1 1]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "uniqueOperationNamesRule" $
+            it "rejects operations with the same name" $
+                let queryString = "query dogOperation {\n\
+                        \  dog {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}\n\
+                        \\n\
+                        \mutation dogOperation {\n\
+                        \  mutateDog {\n\
+                        \    id\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "There can be only one operation named \
+                            \\"dogOperation\"."
+                        , locations = [AST.Location 1 1, AST.Location 7 1]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "uniqueFragmentNamesRule" $
+            it "rejects fragments with the same name" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    ...fragmentOne\n\
+                        \  }\n\
+                        \}\n\
+                        \\n\
+                        \fragment fragmentOne on Dog {\n\
+                        \  name\n\
+                        \}\n\
+                        \\n\
+                        \fragment fragmentOne on Dog {\n\
+                        \  owner {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "There can be only one fragment named \
+                            \\"fragmentOne\"."
+                        , locations = [AST.Location 7 1, AST.Location 11 1]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "fragmentSpreadTargetDefinedRule" $
+            it "rejects the fragment spread without a target" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    ...undefinedFragment\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fragment target \"undefinedFragment\" is \
+                            \undefined."
+                        , locations = [AST.Location 3 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "fragmentSpreadTypeExistenceRule" $ do
+            it "rejects fragment spreads without an unknown target type" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    ...notOnExistingType\n\
+                        \  }\n\
+                        \}\n\
+                        \fragment notOnExistingType on NotInSchema {\n\
+                        \  name\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fragment \"notOnExistingType\" is specified on \
+                            \type \"NotInSchema\" which doesn't exist in the \
+                            \schema."
+                        , locations = [AST.Location 3 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "rejects inline fragments without a target" $
+                let queryString = "{\n\
+                        \  ... on NotInSchema {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Inline fragment is specified on type \
+                            \\"NotInSchema\" which doesn't exist in the schema."
+                        , locations = [AST.Location 2 3]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "fragmentsOnCompositeTypesRule" $ do
+            it "rejects fragments on scalar types" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    ...fragOnScalar\n\
+                        \  }\n\
+                        \}\n\
+                        \fragment fragOnScalar on Int {\n\
+                        \  name\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fragment cannot condition on non composite type \
+                            \\"Int\"."
+                        , locations = [AST.Location 6 1]
+                        }
+                 in validate queryString `shouldContain` [expected]
+
+            it "rejects inline fragments on scalar types" $
+                let queryString = "{\n\
+                        \  ... on Boolean {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fragment cannot condition on non composite type \
+                            \\"Boolean\"."
+                        , locations = [AST.Location 2 3]
+                        }
+                in validate queryString `shouldContain` [expected]
+
+        context "noUnusedFragmentsRule" $
+            it "rejects unused fragments" $
+                let queryString = "fragment nameFragment on Dog { # unused\n\
+                        \  name\n\
+                        \}\n\
+                        \\n\
+                        \{\n\
+                        \  dog {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fragment \"nameFragment\" is never used."
+                        , locations = [AST.Location 1 1]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "noFragmentCyclesRule" $
+            it "rejects spreads that form cycles" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    ...nameFragment\n\
+                        \  }\n\
+                        \}\n\
+                        \fragment nameFragment on Dog {\n\
+                        \  name\n\
+                        \  ...barkVolumeFragment\n\
+                        \}\n\
+                        \fragment barkVolumeFragment on Dog {\n\
+                        \  barkVolume\n\
+                        \  ...nameFragment\n\
+                        \}"
+                    error1 = Error
+                        { message =
+                            "Cannot spread fragment \"barkVolumeFragment\" \
+                            \within itself (via barkVolumeFragment -> \
+                            \nameFragment -> barkVolumeFragment)."
+                        , locations = [AST.Location 10 1]
+                        }
+                    error2 = Error
+                        { message =
+                            "Cannot spread fragment \"nameFragment\" within \
+                            \itself (via nameFragment -> barkVolumeFragment -> \
+                            \nameFragment)."
+                        , locations = [AST.Location 6 1]
+                        }
+                 in validate queryString `shouldBe` [error1, error2]
+
+        context "uniqueArgumentNamesRule" $
+            it "rejects duplicate field arguments" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    isHouseTrained(atOtherHomes: true, atOtherHomes: true)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "There can be only one argument named \
+                            \\"atOtherHomes\"."
+                        , locations = [AST.Location 3 20, AST.Location 3 40]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "uniqueDirectiveNamesRule" $ do
+            it "rejects more than one directive per location" $
+                let queryString = "query ($foo: Boolean = true, $bar: Boolean = false) {\n\
+                        \  dog @skip(if: $foo) @skip(if: $bar) {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "There can be only one directive named \"skip\"."
+                        , locations = [AST.Location 2 7, AST.Location 2 23]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "allows repeating repeatable directives" $
+                let queryString = "query {\n\
+                        \  dog @repeat @repeat {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                 in validate queryString `shouldBe` []
+
+        context "uniqueVariableNamesRule" $
+            it "rejects duplicate variables" $
+                let queryString = "query houseTrainedQuery($atOtherHomes: Boolean, $atOtherHomes: Boolean) {\n\
+                        \  dog {\n\
+                        \    isHouseTrained(atOtherHomes: $atOtherHomes)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "There can be only one variable named \
+                            \\"atOtherHomes\"."
+                        , locations = [AST.Location 1 25, AST.Location 1 49]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "variablesAreInputTypesRule" $
+            it "rejects non-input types as variables" $
+                let queryString = "query takesDogBang($dog: Dog!) {\n\
+                        \  dog {\n\
+                        \    isHouseTrained(atOtherHomes: $dog)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Variable \"$dog\" cannot be non-input type \
+                            \\"Dog\"."
+                        , locations = [AST.Location 1 20]
+                        }
+                 in validate queryString `shouldContain` [expected]
+
+        context "noUndefinedVariablesRule" $ do
+            it "rejects undefined variables" $
+                let queryString = "query variableIsNotDefinedUsedInSingleFragment {\n\
+                        \  dog {\n\
+                        \    ...isHouseTrainedFragment\n\
+                        \  }\n\
+                        \}\n\
+                        \\n\
+                        \fragment isHouseTrainedFragment on Dog {\n\
+                        \  isHouseTrained(atOtherHomes: $atOtherHomes)\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Variable \"$atOtherHomes\" is not defined by \
+                            \operation \
+                            \\"variableIsNotDefinedUsedInSingleFragment\"."
+                        , locations = [AST.Location 8 32]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "gets variable location inside an input object" $
+                let queryString = "query {\n\
+                        \  findDog (complex: { name: $name }) {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message = "Variable \"$name\" is not defined."
+                        , locations = [AST.Location 2 29]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "gets variable location inside an array" $
+                let queryString = "query {\n\
+                        \  findCats (commands: [JUMP, $command]) {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message = "Variable \"$command\" is not defined."
+                        , locations = [AST.Location 2 30]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "noUnusedVariablesRule" $ do
+            it "rejects unused variables" $
+                let queryString = "query variableUnused($atOtherHomes: Boolean) {\n\
+                        \  dog {\n\
+                        \    isHouseTrained\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Variable \"$atOtherHomes\" is never used in \
+                            \operation \"variableUnused\"."
+                        , locations = [AST.Location 1 22]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "detects variables in properties of input objects" $
+                let queryString = "query withVar ($name: String!) {\n\
+                        \  findDog (complex: { name: $name }) {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                 in validate queryString `shouldBe` []
+
+        context "uniqueInputFieldNamesRule" $
+            it "rejects duplicate fields in input objects" $
+                let queryString = "{\n\
+                        \  findDog(complex: { name: \"Fido\", name: \"Jack\" }) {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "There can be only one input field named \"name\"."
+                        , locations = [AST.Location 2 22, AST.Location 2 36]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "fieldsOnCorrectTypeRule" $
+            it "rejects undefined fields" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    meowVolume\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Cannot query field \"meowVolume\" on type \"Dog\"."
+                        , locations = [AST.Location 3 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "scalarLeafsRule" $
+            it "rejects scalar fields with not empty selection set" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    barkVolume {\n\
+                        \      sinceWhen\n\
+                        \    }\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Field \"barkVolume\" must not have a selection \
+                            \since type \"Int\" has no subfields."
+                        , locations = [AST.Location 3 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "knownArgumentNamesRule" $ do
+            it "rejects field arguments missing in the type" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    doesKnowCommand(command: CLEAN_UP_HOUSE, dogCommand: SIT)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Unknown argument \"command\" on field \
+                            \\"Dog.doesKnowCommand\"."
+                        , locations = [AST.Location 3 21]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "rejects directive arguments missing in the definition" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    isHouseTrained(atOtherHomes: true) @include(unless: false, if: true)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Unknown argument \"unless\" on directive \
+                            \\"@include\"."
+                        , locations = [AST.Location 3 49]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "knownDirectiveNamesRule" $
+            it "rejects undefined directives" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    isHouseTrained(atOtherHomes: true) @ignore(if: true)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message = "Unknown directive \"@ignore\"."
+                        , locations = [AST.Location 3 40]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "knownInputFieldNamesRule" $
+            it "rejects undefined input object fields" $
+                let queryString = "{\n\
+                        \  findDog(complex: { favoriteCookieFlavor: \"Bacon\", name: \"Jack\" }) {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Field \"favoriteCookieFlavor\" is not defined \
+                            \by type \"DogData\"."
+                        , locations = [AST.Location 2 22]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "directivesInValidLocationsRule" $
+            it "rejects directives in invalid locations" $
+                let queryString = "query @skip(if: $foo) {\n\
+                        \  dog {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Directive \"@skip\" may not be used on QUERY."
+                        , locations = [AST.Location 1 7]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "overlappingFieldsCanBeMergedRule" $ do
+            it "fails to merge fields of mismatching types" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    name: nickname\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fields \"name\" conflict because \"nickname\" and \
+                            \\"name\" are different fields. Use different \
+                            \aliases on the fields to fetch both if this was \
+                            \intentional."
+                        , locations = [AST.Location 3 5, AST.Location 4 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "fails if the arguments of the same field don't match" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    doesKnowCommand(dogCommand: SIT)\n\
+                        \    doesKnowCommand(dogCommand: HEEL)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fields \"doesKnowCommand\" conflict because they \
+                            \have different arguments. Use different aliases \
+                            \on the fields to fetch both if this was \
+                            \intentional."
+                        , locations = [AST.Location 3 5, AST.Location 4 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "fails to merge same-named field and alias" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    doesKnowCommand(dogCommand: SIT)\n\
+                        \    doesKnowCommand: isHouseTrained(atOtherHomes: true)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fields \"doesKnowCommand\" conflict because \
+                            \\"doesKnowCommand\" and \"isHouseTrained\" are \
+                            \different fields. Use different aliases on the \
+                            \fields to fetch both if this was intentional."
+                        , locations = [AST.Location 3 5, AST.Location 4 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "looks for fields after a successfully merged field pair" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    name\n\
+                        \    doesKnowCommand(dogCommand: SIT)\n\
+                        \  }\n\
+                        \  dog {\n\
+                        \    name\n\
+                        \    doesKnowCommand: isHouseTrained(atOtherHomes: true)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fields \"doesKnowCommand\" conflict because \
+                            \\"doesKnowCommand\" and \"isHouseTrained\" are \
+                            \different fields. Use different aliases on the \
+                            \fields to fetch both if this was intentional."
+                        , locations = [AST.Location 4 5, AST.Location 8 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "possibleFragmentSpreadsRule" $ do
+            it "rejects object inline spreads outside object scope" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    ... on Cat {\n\
+                        \      meowVolume\n\
+                        \    }\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fragment cannot be spread here as objects of type \
+                            \\"Dog\" can never be of type \"Cat\"."
+                        , locations = [AST.Location 3 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "rejects object named spreads outside object scope" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    ... catInDogFragmentInvalid\n\
+                        \  }\n\
+                        \}\n\
+                        \\n\
+                        \fragment catInDogFragmentInvalid on Cat {\n\
+                        \  meowVolume\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Fragment \"catInDogFragmentInvalid\" cannot be \
+                            \spread here as objects of type \"Dog\" can never \
+                            \be of type \"Cat\"."
+                        , locations = [AST.Location 3 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "providedRequiredInputFieldsRule" $
+            it "rejects missing required input fields" $
+                let queryString = "{\n\
+                        \  findDog(complex: { name: null }) {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Input field \"name\" of type \"DogData\" is \
+                            \required, but it was not provided."
+                        , locations = [AST.Location 2 20]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "providedRequiredArgumentsRule" $ do
+            it "checks for (non-)nullable arguments" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    doesKnowCommand(dogCommand: null)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Field \"doesKnowCommand\" argument \"dogCommand\" \
+                            \of type \"DogCommand\" is required, but it was \
+                            \not provided."
+                        , locations = [AST.Location 3 5]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "variablesInAllowedPositionRule" $ do
+            it "rejects wrongly typed variable arguments" $
+                let queryString = "query dogCommandArgQuery($dogCommandArg: DogCommand) {\n\
+                        \  dog {\n\
+                        \    doesKnowCommand(dogCommand: $dogCommandArg)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Variable \"$dogCommandArg\" of type \
+                            \\"DogCommand\" used in position expecting type \
+                            \\"DogCommand!\"."
+                        , locations = [AST.Location 1 26]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "rejects wrongly typed variable arguments" $
+                let queryString = "query intCannotGoIntoBoolean($intArg: Int) {\n\
+                        \  dog {\n\
+                        \    isHouseTrained(atOtherHomes: $intArg)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Variable \"$intArg\" of type \"Int\" used in \
+                            \position expecting type \"Boolean\"."
+                        , locations = [AST.Location 1 30]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+        context "valuesOfCorrectTypeRule" $ do
+            it "rejects values of incorrect types" $
+                let queryString = "{\n\
+                        \  dog {\n\
+                        \    isHouseTrained(atOtherHomes: 3)\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Value 3 cannot be coerced to type \"Boolean\"."
+                        , locations = [AST.Location 3 34]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "uses the location of a single list value" $
+                let queryString = "{\n\
+                        \  cat {\n\
+                        \    doesKnowCommands(catCommands: [3])\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Value 3 cannot be coerced to type \"CatCommand!\"."
+                        , locations = [AST.Location 3 36]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "validates input object properties once" $
+                let queryString = "{\n\
+                        \  findDog(complex: { name: 3 }) {\n\
+                        \    name\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "Value 3 cannot be coerced to type \"String!\"."
+                        , locations = [AST.Location 2 28]
+                        }
+                 in validate queryString `shouldBe` [expected]
+
+            it "checks for required list members" $
+                let queryString = "{\n\
+                        \  cat {\n\
+                        \    doesKnowCommands(catCommands: [null])\n\
+                        \  }\n\
+                        \}"
+                    expected = Error
+                        { message =
+                            "List of non-null values of type \"CatCommand\" \
+                            \cannot contain null values."
+                        , locations = [AST.Location 3 36]
+                        }
+                 in validate queryString `shouldBe` [expected]

tests/Schemas/HeroSchema.hs

@@ -0,0 +1,70 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE OverloadedStrings #-}
+
+module Schemas.HeroSchema (heroSchema) where
+
+import Control.Exception (Exception(..))
+import Control.Monad.Catch (throwM)
+import Language.GraphQL.Error (ResolverException (..))
+import qualified Language.GraphQL.Type.In as In
+import qualified Language.GraphQL.Type as Type
+import Language.GraphQL.Type.Schema (schemaWithTypes)
+import qualified Data.HashMap.Strict as HashMap
+import Data.Typeable (cast)
+import qualified Language.GraphQL.Type.Out as Out
+
+data HeroException = HeroException
+    deriving Show
+
+instance Exception HeroException where
+    toException = toException. ResolverException
+    fromException e = do
+        ResolverException resolverException <- fromException e
+        cast resolverException
+
+heroSchema :: Type.Schema IO
+heroSchema =
+    schemaWithTypes Nothing queryType Nothing Nothing [] mempty
+
+type ObjectType = Out.ObjectType IO
+
+queryType :: ObjectType
+queryType = Out.ObjectType "Query" Nothing []
+    $ HashMap.fromList
+        [ ("hero", Out.ValueResolver heroField heroResolver)
+        ]
+  where
+    heroField = Out.Field Nothing (Out.NamedObjectType heroType)
+        $ HashMap.singleton "id"
+        $ In.Argument Nothing (In.NamedScalarType Type.id) Nothing
+    heroResolver = pure $ Type.Object mempty
+
+stringField :: Out.Field IO
+stringField = Out.Field Nothing (Out.NonNullScalarType Type.string) HashMap.empty
+
+heroType :: ObjectType
+heroType = Out.ObjectType "Hero" Nothing [] $ HashMap.fromList resolvers
+  where
+    resolvers =
+        [ ("id", Out.ValueResolver stringField (pure $ Type.String "4111"))
+        , ("name", Out.ValueResolver stringField (pure $ Type.String "R2D2"))
+        , ("friends", Out.ValueResolver friendsField (pure $ Type.List [luke]))
+        ]
+    friendsField = Out.Field Nothing (Out.ListType $ Out.NonNullObjectType lukeType) HashMap.empty
+    -- This list values are ignored because of current realisation (types and resolvers are the same entity)
+    -- The values from lukeType will be used
+    luke = Type.Object $ HashMap.fromList
+        [ ("id", "dfdfdf")
+        , ("name", "dfdfdff")
+        ]
+
+lukeType :: ObjectType
+lukeType = Out.ObjectType "Luke" Nothing [] $ HashMap.fromList resolvers
+  where
+    resolvers =
+        [ ("id", Out.ValueResolver stringField (pure $ Type.String "1000"))
+        , ("name", Out.ValueResolver stringField (throwM HeroException))
+        ]

tests/Spec.hs

@@ -0,0 +1 @@
+{-# OPTIONS_GHC -F -pgmF hspec-discover #-}

tests/data/kitchen-sink.graphql

@@ -1,38 +0,0 @@
-# Copyright (c) 2015, Facebook, Inc.
-# All rights reserved.
-#
-# This source code is licensed under the BSD-style license found in the
-# LICENSE file in the root directory of this source tree. An additional grant
-# of patent rights can be found in the PATENTS file in the same directory.
-
-query queryName($foo: ComplexType, $site: Site = MOBILE) {
-  whoever123is: node(id: [123, 456]) {
-    id , # Inline test comment
-    ... on User @defer {
-      field2 {
-        id ,
-        alias: field1(first:10, after:$foo,) @include(if: $foo) {
-          id,
-          ...frag
-        }
-      }
-    }
-  }
-}
-
-mutation likeStory {
-  like(story: 123) @defer {
-    story {
-      id
-    }
-  }
-}
-
-fragment frag on Friend {
-  foo(size: $size, bar: $b, obj: {key: "value"})
-}
-
-{
-  unnamed(truthy: true, falsey: false),
-  query
-}

tests/data/kitchen-sink.graphql.golden

@@ -1 +0,0 @@
-Document [DefinitionOperation (Query "queryName" [VariableDefinition (Variable "foo") (TypeNamed (NamedType "ComplexType")) Nothing,VariableDefinition (Variable "site") (TypeNamed (NamedType "Site")) (Just (ValueEnum "MOBILE"))] [] [SelectionField (Field "whoever123is" "node" [Argument "id" (ValueList (ListValue [ValueInt 123,ValueInt 456]))] [] [SelectionField (Field "" "id" [] [] []),SelectionInlineFragment (InlineFragment (NamedType "User") [Directive "defer" []] [SelectionField (Field "" "field2" [] [] [SelectionField (Field "" "id" [] [] []),SelectionField (Field "alias" "field1" [Argument "first" (ValueInt 10),Argument "after" (ValueVariable (Variable "foo"))] [Directive "include" [Argument "if" (ValueVariable (Variable "foo"))]] [SelectionField (Field "" "id" [] [] []),SelectionFragmentSpread (FragmentSpread "frag" [])])])])])]),DefinitionOperation (Mutation "likeStory" [] [] [SelectionField (Field "" "like" [Argument "story" (ValueInt 123)] [Directive "defer" []] [SelectionField (Field "" "story" [] [] [SelectionField (Field "" "id" [] [] [])])])]),DefinitionFragment (FragmentDefinition "frag" (NamedType "Friend") [] [SelectionField (Field "" "foo" [Argument "size" (ValueVariable (Variable "size")),Argument "bar" (ValueVariable (Variable "b")),Argument "obj" (ValueObject (ObjectValue [ObjectField "key" (ValueString "value")]))] [] [])])]

tests/golden.hs

@@ -1,21 +0,0 @@
-{-# LANGUAGE OverloadedStrings #-}
-module Main where
-
-import Control.Monad ((>=>))
-import Data.Attoparsec.Text (parseOnly)
-import Data.ByteString.Lazy.Char8 as B8
-import qualified Data.Text.IO as TIO
-import Test.Tasty (defaultMain)
-import Test.Tasty.Golden (goldenVsString)
-
-import Data.GraphQL.Parser (document)
-
-main :: IO ()
-main = defaultMain
-     $ goldenVsString "kitchen-sink.graphql"
-                      "./tests/data/kitchen-sink.graphql.golden"
-                      (parse "./tests/data/kitchen-sink.graphql")
-  where
-    parse = fmap (parseOnly document) . TIO.readFile
-        >=> pure . either B8.pack (flip B8.snoc '\n' . B8.pack . show)
-