Merge branch 'all-improvements'

This adds general API documentation, a tutorial and error handling.
2016-03-15 14:02:34 +01:00 · 2016-03-15 14:02:34 +01:00 · 77853b17ae
commit 77853b17ae
parent d8a731fe30 61d6af7778
15 changed files with 710 additions and 49 deletions
--- a/Data/GraphQL.hs
+++ b/Data/GraphQL.hs
@ -1,6 +1,7 @@
+-- | This module provides the functions to parse and execute @GraphQL@ queries.
 module Data.GraphQL where

-import Control.Applicative (Alternative, empty)
+import Control.Applicative (Alternative)

 import Data.Text (Text)

@ -11,10 +12,23 @@ import Data.GraphQL.Execute
 import Data.GraphQL.Parser
 import Data.GraphQL.Schema

+import Data.GraphQL.Error
+
+-- | Takes a 'Schema' and text representing a @GraphQL@ request document.
+--   If the text parses correctly as a @GraphQL@ query the query is
+--   executed according to the given 'Schema'.
+--
+--   Returns the response as an @Aeson.@'Aeson.Value'.
 graphql :: (Alternative m, Monad m) => Schema m -> Text -> m Aeson.Value
 graphql = flip graphqlSubs $ const Nothing

+-- | Takes a 'Schema', a variable substitution function and text
+--   representing a @GraphQL@ request document.  If the text parses
+--   correctly as a @GraphQL@ query the substitution is applied to the
+--   query and the query is then executed according to the given 'Schema'.
+--
+--   Returns the response as an @Aeson.@'Aeson.Value'.
 graphqlSubs :: (Alternative m, Monad m) => Schema m -> Subs -> Text -> m Aeson.Value
 graphqlSubs schema f =
-    either (const empty) (execute schema f)
+    either parseError (execute schema f)
  . Attoparsec.parseOnly document
--- a/Data/GraphQL/AST.hs
+++ b/Data/GraphQL/AST.hs
@ -1,3 +1,6 @@
+-- | This module defines an abstract syntax tree for the @GraphQL@ language based on
+--   <https://facebook.github.io/graphql/ Facebook's GraphQL Specification>.
+
 module Data.GraphQL.AST where

 import Data.Int (Int32)
@ -39,11 +42,26 @@ data Selection = SelectionField Field
               | SelectionInlineFragment InlineFragment
                 deriving (Eq,Show)

+-- | A 'SelectionSet' is primarily composed of 'Field's. A 'Field' describes one
+--   discrete piece of information available to request within a 'SelectionSet'.
+--
+--   Some 'Field's describe complex data or relationships to other data. In
+--   order to further explore this data, a 'Field' may itself contain a
+--   'SelectionSet', allowing for deeply nested requests. All @GraphQL@ operations
+--   must specify their 'Selection's down to 'Field's which return scalar values to
+--   ensure an unambiguously shaped response.
+--
+--   <https://facebook.github.io/graphql/#sec-Language.Query-Document.Fields Field Specification>
 data Field = Field Alias Name [Argument] [Directive] SelectionSet
             deriving (Eq,Show)

 type Alias = Name

+-- | 'Field's are conceptually functions which return values, and occasionally accept
+--   'Argument's which alter their behavior. These 'Argument's often map directly to
+--   function arguments within a @GraphQL@ server’s implementation.
+--
+--   <https://facebook.github.io/graphql/#sec-Language.Query-Document.Arguments Argument Specification>
 data Argument = Argument Name Value deriving (Eq,Show)

 -- * Fragments
@ -63,6 +81,15 @@ type TypeCondition = NamedType

 -- * Values

+-- | 'Field' and 'Directive' 'Arguments' accept input values of various literal
+--   primitives; input values can be scalars, enumeration values, lists, or input
+--   objects.
+--
+--   If not defined as constant (for example, in 'DefaultValue'), input values
+--   can be specified as a 'Variable'. List and inputs objects may also contain
+--   'Variable's (unless defined to be constant).
+--
+--   <https://facebook.github.io/graphql/#sec-Input-Values Input Value Specification>
 data Value = ValueVariable Variable
           | ValueInt Int32
           -- GraphQL Float is double precison
--- a/Data/GraphQL/Encoder.hs
+++ b/Data/GraphQL/Encoder.hs
@ -1,5 +1,6 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE OverloadedStrings #-}
+-- | This module defines a printer for the @GraphQL@ language.
 module Data.GraphQL.Encoder where

 #if !MIN_VERSION_base(4,8,0)
--- a/Data/GraphQL/Error.hs
+++ b/Data/GraphQL/Error.hs
@ -0,0 +1,63 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE OverloadedStrings #-}
+module Data.GraphQL.Error (
+  parseError,
+  CollectErrsT,
+  addErr,
+  addErrMsg,
+  runCollectErrs,
+  joinErrs,
+  errWrap
+  ) where
+
+import qualified Data.Aeson as Aeson
+import Data.Text (Text, pack)
+
+import Control.Arrow ((&&&))
+
+#if !MIN_VERSION_base(4,8,0)
+import Control.Applicative (Applicative, pure)
+import Data.Foldable (Foldable, concatMap)
+import Prelude hiding (concatMap)
+#endif
+
+-- | Wraps a parse error into a list of errors.
+parseError :: Applicative f => String -> f Aeson.Value
+parseError s =
+  pure $ Aeson.object [("errors", Aeson.toJSON [makeErrorMsg $ pack s])]
+
+-- | A wrapper for an 'Applicative' to pass error messages around.
+type CollectErrsT f a = f (a,[Aeson.Value])
+
+-- | Takes a (wrapped) list (foldable functor) of values and errors,
+--   joins the values into a list and concatenates the errors.
+joinErrs
+  :: (Functor m, Functor f, Foldable f)
+  => m (f (a,[Aeson.Value])) -> CollectErrsT m (f a)
+joinErrs = fmap $ fmap fst &&& concatMap snd
+
+-- | Wraps the given 'Applicative' to handle errors
+errWrap :: Functor f => f a -> f (a, [Aeson.Value])
+errWrap = fmap (flip (,) [])
+
+-- | Adds an error to the list of errors.
+addErr :: Functor f => Aeson.Value -> CollectErrsT f a -> CollectErrsT f a
+addErr v = (fmap . fmap) (v :)
+
+makeErrorMsg :: Text -> Aeson.Value
+makeErrorMsg s = Aeson.object [("message",Aeson.toJSON s)]
+
+-- | Convenience function for just wrapping an error message.
+addErrMsg :: Functor f => Text -> CollectErrsT f a -> CollectErrsT f a
+addErrMsg = addErr . makeErrorMsg
+
+-- | Runs the given query, but collects the errors into an error
+--   list which is then sent back with the data.
+runCollectErrs :: Functor f => CollectErrsT f Aeson.Value -> f Aeson.Value
+runCollectErrs = fmap finalD
+  where
+    finalD (dat,errs) =
+        Aeson.object
+      $ if null errs
+           then [("data",dat)]
+           else [("data",dat),("errors",Aeson.toJSON $ reverse errs)]
--- a/Data/GraphQL/Execute.hs
+++ b/Data/GraphQL/Execute.hs
@ -1,4 +1,6 @@
 {-# LANGUAGE CPP #-}
+-- | This module provides the function to execute a @GraphQL@ request --
+--   according to a 'Schema'.
 module Data.GraphQL.Execute (execute) where

 #if !MIN_VERSION_base(4,8,0)
@ -13,16 +15,32 @@ import Data.GraphQL.AST
 import Data.GraphQL.Schema (Schema(..))
 import qualified Data.GraphQL.Schema as Schema

-execute
-  :: Alternative f
-  => Schema.Schema f -> Schema.Subs -> Document -> f Aeson.Value
-execute (Schema resolvs) subs = Schema.resolvers resolvs . rootFields subs
+import Data.GraphQL.Error

+-- | Takes a 'Schema', a variable substitution function ('Schema.Subs'), and a
+--   @GraphQL@ 'document'. The substitution is applied to the document using
+--  'rootFields', and the 'Schema''s resolvers are applied to the resulting fields.
+--
+--   Returns the result of the query against the 'Schema' wrapped in a /data/ field, or
+--   errors wrapped in an /errors/ field.
+execute :: Alternative f
+  => Schema.Schema f -> Schema.Subs -> Document -> f Aeson.Value
+execute (Schema resolvs) subs doc = runCollectErrs res
+  where res = Schema.resolvers resolvs $ rootFields subs doc
+
+-- | Takes a variable substitution function and a @GraphQL@ document.
+--   If the document contains one query (and no other definitions)
+--   it applies the substitution to the query's set of selections
+--   and then returns their fields.
 rootFields :: Schema.Subs -> Document -> [Field]
 rootFields subs (Document [DefinitionOperation (Query (Node _varDefs _ _ sels))]) =
    Schema.fields $ substitute subs <$> sels
 rootFields _ _ = []

+-- | Takes a variable substitution function and a selection. If the
+--   selection is a field it applies the substitution to the field's
+--   arguments using 'subsArg', and recursively applies the substitution to
+--   the arguments of fields nested in the primary field.
 substitute :: Schema.Subs -> Selection -> Selection
 substitute subs (SelectionField (Field alias name args directives sels)) =
    SelectionField $ Field
@ -35,6 +53,9 @@ substitute subs (SelectionField (Field alias name args directives sels)) =
 substitute _ sel = sel

 -- TODO: Support different value types
+-- | Takes a variable substitution function and an argument. If the
+--   argument's value is a variable the substitution is applied to the
+--   variable's name.
 subsArg :: Schema.Subs -> Argument -> Maybe Argument
 subsArg subs (Argument n (ValueVariable (Variable v))) =
    Argument n . ValueString <$> subs v
--- a/Data/GraphQL/Parser.hs
+++ b/Data/GraphQL/Parser.hs
@ -1,5 +1,6 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE OverloadedStrings #-}
+-- | This module defines a parser for @GraphQL@ request documents.
 module Data.GraphQL.Parser where

 import Prelude hiding (takeWhile)
--- a/Data/GraphQL/Schema.hs
+++ b/Data/GraphQL/Schema.hs
@ -1,5 +1,8 @@
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE LambdaCase #-}
+-- | This module provides a representation of a @GraphQL@ Schema in addition to
+--   functions for defining and manipulating Schemas.
 module Data.GraphQL.Schema
  ( Schema(..)
  , Resolver
@ -21,14 +24,16 @@ module Data.GraphQL.Schema
  ) where

 #if !MIN_VERSION_base(4,8,0)
-import Control.Applicative (pure, (<|>))
+import Control.Applicative (pure)
+import Control.Arrow (first)
 import Data.Foldable (foldMap)
 import Data.Traversable (traverse)
 import Data.Monoid (Monoid(mempty,mappend))
 #else
+import Data.Bifunctor (first)
 import Data.Monoid (Alt(Alt,getAlt))
 #endif
-import Control.Applicative (Alternative, empty)
+import Control.Applicative (Alternative((<|>), empty))
 import Data.Maybe (catMaybes)
 import Data.Foldable (fold)

@ -36,77 +41,105 @@ import qualified Data.Aeson as Aeson
 import Data.HashMap.Strict (HashMap)
 import qualified Data.HashMap.Strict as HashMap
 import Data.Text (Text)
-import qualified Data.Text as T (null)
+import qualified Data.Text as T (null, unwords)

 import Data.GraphQL.AST
+import Data.GraphQL.Error

+-- | A GraphQL schema.
+--   @f@ is usually expected to be an instance of 'Alternative'.
 data Schema f = Schema [Resolver f]

-type Resolver  f = Field -> f Aeson.Object
+-- | Resolves a 'Field' into an @Aeson.@'Aeson.Object' with error information
+--   (or 'empty'). @f@ is usually expected to be an instance of 'Alternative'.
+type Resolver f = Field -> CollectErrsT f Aeson.Object

+-- | Variable substitution function.
 type Subs = Text -> Maybe Text

+-- | Create a named 'Resolver' from a list of 'Resolver's.
 object :: Alternative f => Text -> [Resolver f] -> Resolver f
 object name resolvs = objectA name $ \case
     [] -> resolvs
     _  -> empty

+-- | Like 'object' but also taking 'Argument's.
 objectA
  :: Alternative f
  => Text -> ([Argument] -> [Resolver f]) -> Resolver f
 objectA name f fld@(Field _ _ args _ sels) =
    withField name (resolvers (f args) $ fields sels) fld

+-- | A scalar represents a primitive value, like a string or an integer.
 scalar :: (Alternative f, Aeson.ToJSON a) => Text -> a -> Resolver f
 scalar name s = scalarA name $ \case
    [] -> pure s
    _  -> empty

+-- | Like 'scalar' but also taking 'Argument's.
 scalarA
  :: (Alternative f, Aeson.ToJSON a)
  => Text -> ([Argument] -> f a) -> Resolver f
-scalarA name f fld@(Field _ _ args _ []) = withField name (f args) fld
+scalarA name f fld@(Field _ _ args _ []) = withField name (errWrap $ f args) fld
 scalarA _ _ _ = empty

+-- | Like 'object' but taking lists of 'Resolver's instead of a single list.
 array :: Alternative f => Text -> [[Resolver f]] -> Resolver f
 array name resolvs = arrayA name $ \case
    [] -> resolvs
    _  -> empty

+-- | Like 'array' but also taking 'Argument's.
 arrayA
  :: Alternative f
  => Text -> ([Argument] -> [[Resolver f]]) -> Resolver f
 arrayA name f fld@(Field _ _ args _ sels) =
-     withField name (traverse (flip resolvers $ fields sels) $ f args) fld
+     withField name (joinErrs $ traverse (flip resolvers $ fields sels) $ f args) fld

+-- | Represents one of a finite set of possible values.
+--   Used in place of a 'scalar' when the possible responses are easily enumerable.
 enum :: Alternative f => Text -> f [Text] -> Resolver f
 enum name enums = enumA name $ \case
     [] -> enums
     _  -> empty

+-- | Like 'enum' but also taking 'Argument's.
 enumA :: Alternative f => Text -> ([Argument] -> f [Text]) -> Resolver f
-enumA name f fld@(Field _ _ args _ []) = withField name (f args) fld
+enumA name f fld@(Field _ _ args _ []) = withField name (errWrap $ f args) fld
 enumA _ _ _ = empty

+-- | Helper function to facilitate 'Argument' handling.
 withField
  :: (Alternative f, Aeson.ToJSON a)
-  => Text -> f a -> Field -> f (HashMap Text Aeson.Value)
+  => Text -> CollectErrsT f a -> Field -> CollectErrsT f (HashMap Text Aeson.Value)
 withField name f (Field alias name' _ _ _) =
     if name == name'
-        then fmap (HashMap.singleton aliasOrName . Aeson.toJSON) f
+        then fmap (first $ HashMap.singleton aliasOrName . Aeson.toJSON) f
        else empty
     where
       aliasOrName = if T.null alias then name' else alias

-resolvers :: Alternative f => [Resolver f] -> [Field] -> f Aeson.Value
+-- | Takes a list of 'Resolver's and a list of 'Field's and applies each
+--   'Resolver' to each 'Field'. Resolves into a value containing the
+--   resolved 'Field', or a null value and error information.
+resolvers :: Alternative f => [Resolver f] -> [Field] -> CollectErrsT f Aeson.Value
 resolvers resolvs =
-    fmap (Aeson.toJSON . fold)
-  . traverse (\fld -> getAlt $ foldMap (Alt . ($ fld)) resolvs)
+    fmap (first Aeson.toJSON . fold)
+  . traverse (\fld -> getAlt (foldMap (Alt . ($ fld)) resolvs) <|> errmsg fld)
+  where
+    errmsg (Field alias name _ _ _) = addErrMsg msg $ (errWrap . pure) val
+       where
+         val = HashMap.singleton aliasOrName Aeson.Null
+         msg = T.unwords ["field", name, "not resolved."]
+         aliasOrName = if T.null alias then name else alias

+-- | Checks whether the given 'Selection' contains a 'Field' and
+--   returns the 'Field' if so, else returns 'Nothing'.
 field :: Selection -> Maybe Field
 field (SelectionField x) = Just x
 field _ = Nothing

+-- | Returns a list of the 'Field's contained in the given 'SelectionSet'.
 fields :: SelectionSet -> [Field]
 fields = catMaybes . fmap field

--- a/docs/tutorial/Makefile
+++ b/docs/tutorial/Makefile
@ -0,0 +1,4 @@
+default:
+	pandoc -f markdown+lhs+yaml_metadata_block --highlight-style=haddock -S -c "https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css" --section-divs -c tutorial.css --toc --standalone -t html5 -o tutorial.html tutorial.lhs
+	pandoc -f markdown+lhs+yaml_metadata_block --highlight-style=haddock --toc --standalone -t rst -o tutorial.rst tutorial.lhs
+	pandoc -f markdown+lhs+yaml_metadata_block --highlight-style=haddock --toc --standalone -t latex -o tutorial.pdf tutorial.lhs
--- a/docs/tutorial/tutorial.css
+++ b/docs/tutorial/tutorial.css
@ -0,0 +1,3 @@
+body {
+    padding: 0 20px;
+}
--- a/docs/tutorial/tutorial.html
+++ b/docs/tutorial/tutorial.html
@ -0,0 +1,165 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <meta name="generator" content="pandoc">
+  <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
+  <title>GraphQL Haskell Tutorial</title>
+  <style type="text/css">code{white-space: pre;}</style>
+  <style type="text/css">
+div.sourceCode { overflow-x: auto; }
+table.sourceCode, tr.sourceCode, td.lineNumbers, td.sourceCode {
+  margin: 0; padding: 0; vertical-align: baseline; border: none; }
+table.sourceCode { width: 100%; line-height: 100%; }
+td.lineNumbers { text-align: right; padding-right: 4px; padding-left: 4px; color: #aaaaaa; border-right: 1px solid #aaaaaa; }
+td.sourceCode { padding-left: 5px; }
+code > span.kw { color: #0000ff; } /* Keyword */
+code > span.ch { color: #008080; } /* Char */
+code > span.st { color: #008080; } /* String */
+code > span.co { color: #008000; } /* Comment */
+code > span.ot { color: #ff4000; } /* Other */
+code > span.al { color: #ff0000; } /* Alert */
+code > span.er { color: #ff0000; font-weight: bold; } /* Error */
+code > span.wa { color: #008000; font-weight: bold; } /* Warning */
+code > span.cn { } /* Constant */
+code > span.sc { color: #008080; } /* SpecialChar */
+code > span.vs { color: #008080; } /* VerbatimString */
+code > span.ss { color: #008080; } /* SpecialString */
+code > span.im { } /* Import */
+code > span.va { } /* Variable */
+code > span.cf { color: #0000ff; } /* ControlFlow */
+code > span.op { } /* Operator */
+code > span.bu { } /* BuiltIn */
+code > span.ex { } /* Extension */
+code > span.pp { color: #ff4000; } /* Preprocessor */
+code > span.do { color: #008000; } /* Documentation */
+code > span.an { color: #008000; } /* Annotation */
+code > span.cv { color: #008000; } /* CommentVar */
+code > span.at { } /* Attribute */
+code > span.in { color: #008000; } /* Information */
+  </style>
+  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
+  <link rel="stylesheet" href="tutorial.css">
+  <!--[if lt IE 9]>
+    <script src="//cdnjs.cloudflare.com/ajax/libs/html5shiv/3.7.3/html5shiv-printshiv.min.js"></script>
+  <![endif]-->
+</head>
+<body>
+<header>
+<h1 class="title">GraphQL Haskell Tutorial</h1>
+</header>
+<nav id="TOC">
+<ul>
+<li><a href="#getting-started">Getting started</a><ul>
+<li><a href="#first-example">First example</a></li>
+<li><a href="#monadic-actions">Monadic actions</a></li>
+<li><a href="#errors">Errors</a></li>
+<li><a href="#combining-resolvers">Combining resolvers</a></li>
+</ul></li>
+<li><a href="#further-examples">Further examples</a></li>
+</ul>
+</nav>
+<section id="getting-started" class="level2">
+<h2>Getting started</h2>
+<p>Welcome to graphql-haskell!</p>
+<p>We have written a small tutorial to help you (and ourselves) understand the graphql package.</p>
+<p>Since this file is a literate haskell file, we start by importing some dependencies.</p>
+<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">{-# LANGUAGE OverloadedStrings #-}</span>
+<span class="ot">{-# LANGUAGE LambdaCase #-}</span>
+<span class="kw">module</span> <span class="dt">Main</span> <span class="kw">where</span>
+
+<span class="kw">import </span><span class="dt">Prelude</span> <span class="kw">hiding</span> (empty, putStrLn)
+<span class="kw">import </span><span class="dt">Data.GraphQL</span>
+<span class="kw">import </span><span class="dt">Data.GraphQL.Schema</span>
+<span class="kw">import qualified</span> <span class="dt">Data.GraphQL.Schema</span> <span class="kw">as</span> <span class="dt">Schema</span>
+
+<span class="kw">import </span><span class="dt">Control.Applicative</span>
+<span class="kw">import </span><span class="dt">Data.Text</span> <span class="kw">hiding</span> (empty)
+<span class="kw">import </span><span class="dt">Data.Aeson</span>
+<span class="kw">import </span><span class="dt">Data.ByteString.Lazy.Char8</span> (putStrLn)
+
+<span class="kw">import </span><span class="dt">Data.Time</span>
+
+<span class="kw">import </span><span class="dt">Debug.Trace</span></code></pre></div>
+<section id="first-example" class="level3">
+<h3>First example</h3>
+<p>Now, as our first example, we are going to look at the example from <a href="https://github.com/graphql/graphql-js">graphql.js</a>.</p>
+<p>First we build a GraphQL schema.</p>
+<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">schema1 ::</span> <span class="dt">Alternative</span> f <span class="ot">=&gt;</span> <span class="dt">Schema</span> f
+schema1 <span class="fu">=</span> <span class="dt">Schema</span> [hello]
+
+<span class="ot">hello ::</span> <span class="dt">Alternative</span> f <span class="ot">=&gt;</span> <span class="dt">Resolver</span> f
+hello <span class="fu">=</span> Schema.scalar <span class="st">&quot;hello&quot;</span> (<span class="st">&quot;it&#39;s me&quot;</span><span class="ot"> ::</span> <span class="dt">Text</span>)</code></pre></div>
+<p>This defines a simple schema with one type and one field, that resolves to a fixed value.</p>
+<p>Next we define our query.</p>
+<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">query1 ::</span> <span class="dt">Text</span>
+query1 <span class="fu">=</span> <span class="st">&quot;{ hello }&quot;</span></code></pre></div>
+<p>To run the query, we call the <code>graphql</code> with the schema and the query.</p>
+<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">main1 ::</span> <span class="dt">IO</span> ()
+main1 <span class="fu">=</span> putStrLn <span class="fu">=&lt;&lt;</span> encode <span class="fu">&lt;$&gt;</span> graphql schema1 query1</code></pre></div>
+<p>This runs the query by fetching the one field defined, returning</p>
+<p><code>{&quot;data&quot; : {&quot;hello&quot;:&quot;it's me&quot;}}</code></p>
+</section>
+<section id="monadic-actions" class="level3">
+<h3>Monadic actions</h3>
+<p>For this example, we’re going to be using time.</p>
+<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">schema2 ::</span> <span class="dt">Schema</span> <span class="dt">IO</span>
+schema2 <span class="fu">=</span> <span class="dt">Schema</span> [time]
+
+<span class="ot">time ::</span> <span class="dt">Resolver</span> <span class="dt">IO</span>
+time <span class="fu">=</span> Schema.scalarA <span class="st">&quot;time&quot;</span> <span class="fu">$</span> \<span class="kw">case</span>
+  [] <span class="ot">-&gt;</span> <span class="kw">do</span> t <span class="ot">&lt;-</span> getCurrentTime
+           return <span class="fu">$</span> show t
+  _  <span class="ot">-&gt;</span> empty</code></pre></div>
+<p>This defines a simple schema with one type and one field, which resolves to the current time.</p>
+<p>Next we define our query.</p>
+<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">query2 ::</span> <span class="dt">Text</span>
+query2 <span class="fu">=</span> <span class="st">&quot;{ time }&quot;</span>
+
+<span class="ot">main2 ::</span> <span class="dt">IO</span> ()
+main2 <span class="fu">=</span> putStrLn <span class="fu">=&lt;&lt;</span> encode <span class="fu">&lt;$&gt;</span> graphql schema2 query2</code></pre></div>
+<p>This runs the query, returning the current time</p>
+<p><code>{&quot;data&quot;: {&quot;time&quot;:&quot;2016-03-08 23:28:14.546899 UTC&quot;}}</code></p>
+</section>
+<section id="errors" class="level3">
+<h3>Errors</h3>
+<p>Errors are handled according to the spec, with fields that cause erros being resolved to <code>null</code>, and an error being added to the error list.</p>
+<p>An example of this is the following query:</p>
+<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">queryShouldFail ::</span> <span class="dt">Text</span>
+queryShouldFail <span class="fu">=</span> <span class="st">&quot;{ boyhowdy }&quot;</span></code></pre></div>
+<p>Since there is no <code>boyhowdy</code> field in our schema, it will not resolve, and the query will fail, as we can see in the following example.</p>
+<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">mainShouldFail ::</span> <span class="dt">IO</span> ()
+mainShouldFail <span class="fu">=</span> <span class="kw">do</span>
+  r <span class="ot">&lt;-</span> graphql schema1 query1
+  putStrLn <span class="fu">$</span> encode r
+  putStrLn <span class="st">&quot;This will fail&quot;</span>
+  r <span class="ot">&lt;-</span> graphql schema1 queryShouldFail
+  putStrLn <span class="fu">$</span> encode r</code></pre></div>
+<p>This outputs:</p>
+<pre><code>{&quot;data&quot;: {&quot;hello&quot;: &quot;it&#39;s me&quot;}}
+This will fail
+{&quot;data&quot;: {&quot;boyhowdy&quot;: null}, &quot;errors&quot;:[{&quot;message&quot;: &quot;the field boyhowdy did not resolve.&quot;}]}</code></pre>
+</section>
+<section id="combining-resolvers" class="level3">
+<h3>Combining resolvers</h3>
+<p>Now that we have two resolvers, we can define a schema which uses them both.</p>
+<div class="sourceCode"><pre class="sourceCode literate haskell"><code class="sourceCode haskell"><span class="ot">schema3 ::</span> <span class="dt">Schema</span> <span class="dt">IO</span>
+schema3 <span class="fu">=</span> <span class="dt">Schema</span> [hello, time]
+
+<span class="ot">query3 ::</span> <span class="dt">Text</span>
+query3 <span class="fu">=</span> <span class="st">&quot;query timeAndHello { time hello }&quot;</span>
+
+<span class="ot">main3 ::</span> <span class="dt">IO</span> ()
+main3 <span class="fu">=</span> putStrLn <span class="fu">=&lt;&lt;</span> encode <span class="fu">&lt;$&gt;</span> graphql schema3 query3</code></pre></div>
+<p>This queries for both time and hello, returning</p>
+<p><code>{ &quot;data&quot;: {&quot;hello&quot;:&quot;it's me&quot;,&quot;time&quot;:&quot;2016-03-08 23:29:11.62108 UTC&quot;}}</code></p>
+<p>Notice that we can name our queries, as we did with <code>timeAndHello</code>. Since we have only been using single queries, we can use the shorthand <code>{ time hello}</code>, as we have been doing in the previous examples.</p>
+<p>In GraphQL there can only be one operation per query.</p>
+</section>
+</section>
+<section id="further-examples" class="level2">
+<h2>Further examples</h2>
+<p>More examples on queries and a more complex schema can be found in the test directory, in the <a href="../../tests/Test/StarWars">Test.StarWars</a> module. This includes a more complex schema, and more complex queries.</p>
+</section>
+</body>
+</html>
--- a/docs/tutorial/tutorial.lhs
+++ b/docs/tutorial/tutorial.lhs
@ -0,0 +1,150 @@
+---
+title: GraphQL Haskell Tutorial
+---
+
+
+== Getting started ==
+
+Welcome to graphql-haskell!
+
+We have written a small tutorial to help you (and ourselves) understand the graphql package.
+
+Since this file is a literate haskell file, we start by importing some dependencies.
+
+> {-# LANGUAGE OverloadedStrings #-}
+> {-# LANGUAGE LambdaCase #-}
+> module Main where
+>
+> import Prelude hiding (empty, putStrLn)
+> import Data.GraphQL
+> import Data.GraphQL.Schema
+> import qualified Data.GraphQL.Schema as Schema
+>
+> import Control.Applicative
+> import Data.Text hiding (empty)
+> import Data.Aeson
+> import Data.ByteString.Lazy.Char8 (putStrLn)
+>
+> import Data.Time
+>
+> import Debug.Trace
+
+=== First example ===
+
+Now, as our first example, we are going to look at the
+example from [graphql.js](https://github.com/graphql/graphql-js).
+
+First we build a GraphQL schema.
+
+> schema1 :: Alternative f => Schema f
+> schema1 = Schema [hello]
+>
+> hello :: Alternative f => Resolver f
+> hello = Schema.scalar "hello" ("it's me" :: Text)
+
+This defines a simple schema with one type and one field, that resolves to a fixed value.
+
+Next we define our query.
+
+> query1 :: Text
+> query1 = "{ hello }"
+
+
+To run the query, we call the `graphql` with the schema and the query.
+
+> main1 :: IO ()
+> main1 = putStrLn =<< encode <$> graphql schema1 query1
+
+This runs the query by fetching the one field defined,
+returning
+
+```{"data" : {"hello":"it's me"}}```
+
+
+
+=== Monadic actions ===
+
+For this example, we're going to be using time.
+
+> schema2 :: Schema IO
+> schema2 = Schema [time]
+>
+> time :: Resolver IO
+> time = Schema.scalarA "time" $ \case
+>   [] -> do t <- getCurrentTime
+>            return $ show t
+>   _  -> empty
+
+This defines a simple schema with one type and one field,
+which resolves to the current time.
+
+Next we define our query.
+
+> query2 :: Text
+> query2 = "{ time }"
+>
+> main2 :: IO ()
+> main2 = putStrLn =<< encode <$> graphql schema2 query2
+
+This runs the query, returning the current time
+
+```{"data": {"time":"2016-03-08 23:28:14.546899 UTC"}}```
+
+
+=== Errors ===
+
+Errors are handled according to the spec,
+with fields that cause erros being resolved to `null`,
+and an error being added to the error list.
+
+An example of this is the following query:
+
+> queryShouldFail :: Text
+> queryShouldFail = "{ boyhowdy }"
+
+Since there is no `boyhowdy` field in our schema, it will not resolve,
+and the query will fail, as we can see in the following example.
+
+> mainShouldFail :: IO ()
+> mainShouldFail = do
+>   r <- graphql schema1 query1
+>   putStrLn $ encode r
+>   putStrLn "This will fail"
+>   r <- graphql schema1 queryShouldFail
+>   putStrLn $ encode r
+>
+
+This outputs:
+
+```
+{"data": {"hello": "it's me"}}
+This will fail
+{"data": {"boyhowdy": null}, "errors":[{"message": "the field boyhowdy did not resolve."}]}
+```
+
+=== Combining resolvers ===
+
+Now that we have two resolvers, we can define a schema which uses them both.
+
+> schema3 :: Schema IO
+> schema3 = Schema [hello, time]
+>
+> query3 :: Text
+> query3 = "query timeAndHello { time hello }"
+>
+> main3 :: IO ()
+> main3 = putStrLn =<< encode <$> graphql schema3 query3
+
+This queries for both time and hello, returning
+
+```{ "data": {"hello":"it's me","time":"2016-03-08 23:29:11.62108 UTC"}}```
+
+Notice that we can name our queries, as we did with `timeAndHello`. Since we have only been using single queries, we can use the shorthand `{ time hello}`, as we have been doing in the previous examples.
+
+In GraphQL there can only be one operation per query.
+
+
+== Further examples ==
+
+More examples on queries and a more complex schema can be found in the test directory,
+in the [Test.StarWars](../../tests/Test/StarWars) module. This includes a more complex schema, and more complex queries.
--- a/docs/tutorial/tutorial.pdf
+++ b/docs/tutorial/tutorial.pdf
--- a/docs/tutorial/tutorial.rst
+++ b/docs/tutorial/tutorial.rst
@ -0,0 +1,176 @@
+========================
+GraphQL Haskell Tutorial
+========================
+
+.. contents::
+   :depth: 3
+..
+
+Getting started
+===============
+
+Welcome to graphql-haskell!
+
+We have written a small tutorial to help you (and ourselves) understand
+the graphql package.
+
+Since this file is a literate haskell file, we start by importing some
+dependencies.
+
+.. code:: haskell
+
+    {-# LANGUAGE OverloadedStrings #-}
+    {-# LANGUAGE LambdaCase #-}
+    module Main where
+
+    import Prelude hiding (empty, putStrLn)
+    import Data.GraphQL
+    import Data.GraphQL.Schema
+    import qualified Data.GraphQL.Schema as Schema
+
+    import Control.Applicative
+    import Data.Text hiding (empty)
+    import Data.Aeson
+    import Data.ByteString.Lazy.Char8 (putStrLn)
+
+    import Data.Time
+
+    import Debug.Trace
+
+First example
+-------------
+
+Now, as our first example, we are going to look at the example from
+`graphql.js <https://github.com/graphql/graphql-js>`__.
+
+First we build a GraphQL schema.
+
+.. code:: haskell
+
+    schema1 :: Alternative f => Schema f
+    schema1 = Schema [hello]
+
+    hello :: Alternative f => Resolver f
+    hello = Schema.scalar "hello" ("it's me" :: Text)
+
+This defines a simple schema with one type and one field, that resolves
+to a fixed value.
+
+Next we define our query.
+
+.. code:: haskell
+
+    query1 :: Text
+    query1 = "{ hello }"
+
+To run the query, we call the ``graphql`` with the schema and the query.
+
+.. code:: haskell
+
+    main1 :: IO ()
+    main1 = putStrLn =<< encode <$> graphql schema1 query1
+
+This runs the query by fetching the one field defined, returning
+
+``{"data" : {"hello":"it's me"}}``
+
+Monadic actions
+---------------
+
+For this example, we're going to be using time.
+
+.. code:: haskell
+
+    schema2 :: Schema IO
+    schema2 = Schema [time]
+
+    time :: Resolver IO
+    time = Schema.scalarA "time" $ \case
+      [] -> do t <- getCurrentTime
+               return $ show t
+      _  -> empty
+
+This defines a simple schema with one type and one field, which resolves
+to the current time.
+
+Next we define our query.
+
+.. code:: haskell
+
+    query2 :: Text
+    query2 = "{ time }"
+
+    main2 :: IO ()
+    main2 = putStrLn =<< encode <$> graphql schema2 query2
+
+This runs the query, returning the current time
+
+``{"data": {"time":"2016-03-08 23:28:14.546899 UTC"}}``
+
+Errors
+------
+
+Errors are handled according to the spec, with fields that cause erros
+being resolved to ``null``, and an error being added to the error list.
+
+An example of this is the following query:
+
+.. code:: haskell
+
+    queryShouldFail :: Text
+    queryShouldFail = "{ boyhowdy }"
+
+Since there is no ``boyhowdy`` field in our schema, it will not resolve,
+and the query will fail, as we can see in the following example.
+
+.. code:: haskell
+
+    mainShouldFail :: IO ()
+    mainShouldFail = do
+      r <- graphql schema1 query1
+      putStrLn $ encode r
+      putStrLn "This will fail"
+      r <- graphql schema1 queryShouldFail
+      putStrLn $ encode r
+
+This outputs:
+
+::
+
+    {"data": {"hello": "it's me"}}
+    This will fail
+    {"data": {"boyhowdy": null}, "errors":[{"message": "the field boyhowdy did not resolve."}]}
+
+Combining resolvers
+-------------------
+
+Now that we have two resolvers, we can define a schema which uses them
+both.
+
+.. code:: haskell
+
+    schema3 :: Schema IO
+    schema3 = Schema [hello, time]
+
+    query3 :: Text
+    query3 = "query timeAndHello { time hello }"
+
+    main3 :: IO ()
+    main3 = putStrLn =<< encode <$> graphql schema3 query3
+
+This queries for both time and hello, returning
+
+``{ "data": {"hello":"it's me","time":"2016-03-08 23:29:11.62108 UTC"}}``
+
+Notice that we can name our queries, as we did with ``timeAndHello``.
+Since we have only been using single queries, we can use the shorthand
+``{ time hello}``, as we have been doing in the previous examples.
+
+In GraphQL there can only be one operation per query.
+
+Further examples
+================
+
+More examples on queries and a more complex schema can be found in the
+test directory, in the `Test.StarWars <../../tests/Test/StarWars>`__
+module. This includes a more complex schema, and more complex queries.
--- a/graphql.cabal
+++ b/graphql.cabal
@ -16,6 +16,7 @@ build-type:          Simple
 cabal-version:       >=1.10
 tested-with:         GHC == 7.8.4, GHC == 7.10.3
 extra-source-files:  README.md CHANGELOG.md stack.yaml
+                     docs/tutorial/tutorial.lhs
 data-files:          tests/data/*.graphql
                     tests/data/*.min.graphql

@ -28,10 +29,11 @@ library
                       Data.GraphQL.Execute
                       Data.GraphQL.Schema
                       Data.GraphQL.Parser
-  build-depends:       base >= 4.7 && < 5,
-                       text >= 0.11.3.1,
-                       aeson >= 0.7.0.3,
+                       Data.GraphQL.Error
+  build-depends:       aeson >= 0.7.0.3,
                       attoparsec >= 0.10.4.0,
+                       base >= 4.7 && < 5,
+                       text >= 0.11.3.1,
                       unordered-containers >= 0.2.5.0

 test-suite tasty
@ -44,15 +46,15 @@ test-suite tasty
                       Test.StarWars.Data
                       Test.StarWars.Schema
                       Test.StarWars.QueryTests
-  build-depends:       base >= 4.6 && <5,
-                       aeson >= 0.7.0.3,
-                       text >= 0.11.3.1,
+  build-depends:       aeson >= 0.7.0.3,
                       attoparsec >= 0.10.4.0,
+                       base >= 4.6 && <5,
+                       graphql,
                       raw-strings-qq >= 1.1,
                       tasty >= 0.10,
                       tasty-hunit >= 0.9,
-                       unordered-containers >= 0.2.5.0,
-                       graphql
+                       text >= 0.11.3.1,
+                       unordered-containers >= 0.2.5.0

 source-repository head
  type:     git
--- a/tests/Test/StarWars/QueryTests.hs
+++ b/tests/Test/StarWars/QueryTests.hs
@ -2,7 +2,7 @@
 {-# LANGUAGE QuasiQuotes #-}
 module Test.StarWars.QueryTests (test) where

-import qualified Data.Aeson as Aeson (Value)
+import qualified Data.Aeson as Aeson (Value(Null), toJSON)
 import Data.Aeson (object, (.=))
 import Data.Text (Text)
 import Text.RawString.QQ (r)
@ -28,7 +28,7 @@ test = testGroup "Star Wars Query Tests"
              }
            }
        |]
-      $ object ["hero" .= object ["id" .= ("2001" :: Text)]]
+      $ object [ "data" .= object ["hero" .= object ["id" .= ("2001" :: Text)]]]
    , testCase "R2-D2 ID and friends" . testQuery
        [r| query HeroNameAndFriendsQuery {
              hero {
@ -40,7 +40,7 @@ test = testGroup "Star Wars Query Tests"
              }
            }
        |]
-      $ object [
+      $ object [ "data" .= object [
          "hero" .= object [
              "id" .= ("2001" :: Text)
            , "name" .= ("R2-D2" :: Text)
@ -50,7 +50,7 @@ test = testGroup "Star Wars Query Tests"
                , object ["name" .= ("Leia Organa" :: Text)]
                ]
            ]
-        ]
+        ]]
    ]
  , testGroup "Nested Queries"
    [ testCase "R2-D2 friends" . testQuery
@ -67,7 +67,7 @@ test = testGroup "Star Wars Query Tests"
              }
            }
        |]
-      $ object [
+      $ object [ "data" .= object [
          "hero" .= object [
              "name" .= ("R2-D2" :: Text)
            , "friends" .= [
@ -102,7 +102,7 @@ test = testGroup "Star Wars Query Tests"
                    ]
                ]
            ]
-        ]
+        ]]
    , testCase "Luke ID" . testQuery
        [r| query FetchLukeQuery {
              human(id: "1000") {
@ -110,12 +110,12 @@ test = testGroup "Star Wars Query Tests"
              }
            }
        |]
-      $ object [
+      $ object [ "data" .= object [
          "human" .= object [
             "name" .= ("Luke Skywalker" :: Text)
          ]
        ]
-    ]
+    ]]
    , testCase "Luke ID with variable" . testQueryParams
         (\v -> if v == "someId"
                   then Just "1000"
@ -126,9 +126,9 @@ test = testGroup "Star Wars Query Tests"
               }
             }
         |]
-      $ object [
+      $ object [ "data" .= object [
          "human" .= object ["name" .= ("Luke Skywalker" :: Text)]
-        ]
+        ]]
    , testCase "Han ID with variable" . testQueryParams
        (\v -> if v == "someId"
                  then Just "1002"
@ -139,10 +139,10 @@ test = testGroup "Star Wars Query Tests"
              }
            }
        |]
-      $ object [
+      $ object [ "data" .= object [
          "human" .= object ["name" .= ("Han Solo" :: Text)]
-        ]
-    , testCase "Invalid ID" $ testFailParams
+        ]]
+    , testCase "Invalid ID" . testQueryParams
        (\v -> if v == "id"
                  then Just "Not a valid ID"
                  else Nothing)
@ -151,13 +151,14 @@ test = testGroup "Star Wars Query Tests"
                name
              }
            }
-        |]
+        |] $ object ["data" .= object ["human" .= object ["name" .= Aeson.Null]],
+                     "errors" .= (Aeson.toJSON [object ["message" .= ("field name not resolved." :: Text)]])]
        -- TODO: This test is directly ported from `graphql-js`, however do we want
        -- to mimic the same behavior? Is this part of the spec? Once proper
        -- exceptions are implemented this test might no longer be meaningful.
        -- If the same behavior needs to be replicated, should it be implemented
        -- when defining the `Schema` or when executing?
-        -- $ object ["human" .= Aeson.Null]
+        -- $ object [ "data" .= object ["human" .= Aeson.Null] ]
    , testCase "Luke aliased" . testQuery
        [r| query FetchLukeAliased {
              luke: human(id: "1000") {
@ -165,11 +166,11 @@ test = testGroup "Star Wars Query Tests"
              }
            }
        |]
-      $ object [
+      $ object [ "data" .= object [
         "luke" .= object [
           "name" .= ("Luke Skywalker" :: Text)
           ]
-        ]
+        ]]
    , testCase "R2-D2 ID and friends aliased" . testQuery
        [r| query HeroNameAndFriendsQuery {
              hero {
@ -181,7 +182,7 @@ test = testGroup "Star Wars Query Tests"
              }
            }
        |]
-      $ object [
+      $ object [ "data" .= object [
          "hero" .= object [
              "id" .= ("2001" :: Text)
            , "name" .= ("R2-D2" :: Text)
@ -191,7 +192,7 @@ test = testGroup "Star Wars Query Tests"
                , object ["friendName" .= ("Leia Organa" :: Text)]
                ]
            ]
-        ]
+        ]]
    , testCase "Luke and Leia aliased" . testQuery
        [r| query FetchLukeAndLeiaAliased {
              luke: human(id: "1000") {
@ -202,14 +203,14 @@ test = testGroup "Star Wars Query Tests"
              }
            }
        |]
-      $ object [
+      $ object [ "data" .= object [
          "luke" .= object [
            "name" .= ("Luke Skywalker" :: Text)
           ]
        , "leia" .= object [
            "name" .= ("Leia Organa" :: Text)
           ]
-        ]
+        ]]
  ]

 testQuery :: Text -> Aeson.Value -> Assertion
@ -221,5 +222,5 @@ testQuery q expected = graphql schema q @?= Just expected
 testQueryParams :: Subs -> Text -> Aeson.Value -> Assertion
 testQueryParams f q expected = graphqlSubs schema f q @?= Just expected

-testFailParams :: Subs -> Text -> Assertion
-testFailParams f q = graphqlSubs schema f q @?= Nothing
+-- testFailParams :: Subs -> Text -> Assertion
+-- testFailParams f q = graphqlSubs schema f q @?= Nothing