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Replace Alternative with MonadPlus

This commit is contained in:
Eugen Wissner 2019-06-28 11:12:28 +02:00
parent ae4038eb47
commit 79c734fa62
7 changed files with 115 additions and 100 deletions
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6
Data/GraphQL.hs
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@ -1,7 +1,7 @@
-- | This module provides the functions to parse and execute @GraphQL@ queries.
module Data.GraphQL where
import Control.Applicative (Alternative)
import Control.Monad (MonadPlus)
import qualified Data.Text as T
@ -21,7 +21,7 @@ import Data.GraphQL.Error
-- executed according to the given 'Schema'.
--
-- Returns the response as an @Aeson.@'Aeson.Value'.
graphql :: (Alternative m, Monad m) => Schema m -> T.Text -> m Aeson.Value
graphql :: MonadPlus m => Schema m -> T.Text -> m Aeson.Value
graphql = flip graphqlSubs $ const Nothing
-- | Takes a 'Schema', a variable substitution function and text
@ -30,7 +30,7 @@ graphql = flip graphqlSubs $ const Nothing
-- 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 -> T.Text -> m Aeson.Value
graphqlSubs :: MonadPlus m => Schema m -> Subs -> T.Text -> m Aeson.Value
graphqlSubs schema f =
either (parseError . errorBundlePretty) (execute schema f)
. parse document ""

76
Data/GraphQL/Error.hs
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@ -1,57 +1,57 @@
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TupleSections #-}
module Data.GraphQL.Error (
parseError,
CollectErrsT,
addErr,
addErrMsg,
runCollectErrs,
joinErrs,
errWrap
module Data.GraphQL.Error
( parseError
, CollectErrsT
, addErr
, addErrMsg
, runCollectErrs
, runAppendErrs
) where
import qualified Data.Aeson as Aeson
import Data.Text (Text, pack)
import Control.Arrow ((&&&))
import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.State ( StateT
, modify
, runStateT
)
-- | 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 (, [])
-- | A wrapper to pass error messages around.
type CollectErrsT m = StateT [Aeson.Value] m
-- | Adds an error to the list of errors.
addErr :: Functor f => Aeson.Value -> CollectErrsT f a -> CollectErrsT f a
addErr v = (fmap . fmap) (v :)
addErr :: Monad m => Aeson.Value -> CollectErrsT m ()
addErr v = modify (v :)
makeErrorMsg :: Text -> Aeson.Value
makeErrorMsg s = Aeson.object [("message",Aeson.toJSON s)]
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 :: Monad m => Text -> CollectErrsT m ()
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)]
-- | Appends the given list of errors to the current list of errors.
appendErrs :: Monad m => [Aeson.Value] -> CollectErrsT m ()
appendErrs errs = modify (errs ++)
-- | Runs the given query computation, but collects the errors into an error
-- list, which is then sent back with the data.
runCollectErrs :: Monad m => CollectErrsT m Aeson.Value -> m Aeson.Value
runCollectErrs res = do
(dat, errs) <- runStateT res []
if null errs
then return $ Aeson.object [("data", dat)]
else return $ Aeson.object [("data", dat), ("errors", Aeson.toJSON $ reverse errs)]
-- | Runs the given computation, collecting the errors and appending them
-- to the previous list of errors.
runAppendErrs :: Monad m => CollectErrsT m a -> CollectErrsT m a
runAppendErrs f = do
(v, errs) <- lift $ runStateT f []
appendErrs errs
return v

14
Data/GraphQL/Execute.hs
View File

@ -3,7 +3,7 @@
-- according to a 'Schema'.
module Data.GraphQL.Execute (execute) where
import Control.Applicative (Alternative, empty)
import Control.Monad (MonadPlus(..))
import Data.GraphQL.Error
import qualified Data.List.NonEmpty as NE
import Data.List.NonEmpty (NonEmpty((:|)))
@ -21,15 +21,17 @@ import qualified Data.GraphQL.Schema as Schema
-- Returns the result of the query against the 'Schema' wrapped in a /data/ field, or
-- errors wrapped in an /errors/ field.
execute
:: (Alternative f, Monad f)
=> Schema f -> Schema.Subs -> AST.Document -> f Aeson.Value
execute schema subs doc = document schema =<< maybe empty pure (Transform.document subs doc)
:: (MonadPlus m)
=> Schema m -> Schema.Subs -> AST.Document -> m Aeson.Value
execute schema subs doc = do
coreDocument <- maybe mzero pure (Transform.document subs doc)
document schema coreDocument
document :: Alternative f => Schema f -> AST.Core.Document -> f Aeson.Value
document :: MonadPlus m => Schema m -> AST.Core.Document -> m Aeson.Value
document schema (op :| []) = operation schema op
document _ _ = error "Multiple operations not supported yet"
operation :: Alternative f => Schema f -> AST.Core.Operation -> f Aeson.Value
operation :: MonadPlus m => Schema m -> AST.Core.Operation -> m Aeson.Value
operation schema (AST.Core.Query flds)
= runCollectErrs (Schema.resolve (NE.toList schema) (NE.toList flds))
operation schema (AST.Core.Mutation flds)

93
Data/GraphQL/Schema.hs
View File

@ -25,13 +25,17 @@ module Data.GraphQL.Schema
, Value(..)
) where
import Control.Applicative (Alternative(empty), (<|>))
import Data.Bifunctor (first)
import Control.Applicative (Alternative(..))
import Control.Monad (MonadPlus)
import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.State ( get
, put
)
import Data.Foldable (fold)
import Data.GraphQL.Error
import Data.List.NonEmpty (NonEmpty)
import Data.Maybe (fromMaybe)
import Data.Monoid (Alt(Alt,getAlt))
import Data.Monoid (Alt(..))
import qualified Data.Aeson as Aeson
import Data.HashMap.Strict (HashMap)
import qualified Data.HashMap.Strict as HashMap
@ -41,13 +45,13 @@ import Data.GraphQL.AST.Core
-- | A GraphQL schema.
-- @f@ is usually expected to be an instance of 'Alternative'.
type Schema f = NonEmpty (Resolver f)
type Schema m = NonEmpty (Resolver m)
-- | 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
type Resolver m = Field -> CollectErrsT m Aeson.Object
type Resolvers f = [Resolver f]
type Resolvers m = [Resolver m]
type Fields = [Field]
@ -57,107 +61,108 @@ type Arguments = [Argument]
type Subs = Name -> Maybe Value
-- | Create a new 'Resolver' with the given 'Name' from the given 'Resolver's.
object :: Alternative f => Name -> Resolvers f -> Resolver f
object :: MonadPlus m => Name -> Resolvers m -> Resolver m
object name resolvers = objectA name $ \case
[] -> resolvers
_ -> empty
-- | Like 'object' but also taking 'Argument's.
objectA
:: Alternative f
=> Name -> (Arguments -> Resolvers f) -> Resolver f
:: MonadPlus m
=> Name -> (Arguments -> Resolvers m) -> Resolver m
objectA name f fld@(Field _ _ args flds) = withField name (resolve (f args) flds) fld
-- | Create a named 'Resolver' from a list of 'Resolver's.
object' :: (Alternative f, Monad f) => T.Text -> f [Resolver f] -> Resolver f
object' :: MonadPlus m => Name -> m (Resolvers m) -> Resolver m
object' name resolvs = objectA' name $ \case
[] -> resolvs
_ -> empty
-- | Like 'object'' but also taking 'Argument's.
objectA'
:: (Alternative f, Monad f)
=> T.Text -> ([Argument] -> f [Resolver f]) -> Resolver f
:: MonadPlus m
=> Name -> (Arguments -> m (Resolvers m)) -> Resolver m
objectA' name f fld@(Field _ _ args flds) = do
resolvs <- f args
resolvs <- lift $ f args
withField name (resolve resolvs flds) fld
-- | A scalar represents a primitive value, like a string or an integer.
scalar :: (Alternative f, Aeson.ToJSON a) => Name -> a -> Resolver f
scalar :: (MonadPlus m, Aeson.ToJSON a) => Name -> a -> Resolver m
scalar name s = scalarA name $ \case
[] -> pure s
_ -> empty
-- | Like 'scalar' but also taking 'Argument's.
scalarA
:: (Alternative f, Aeson.ToJSON a)
=> Name -> (Arguments -> f a) -> Resolver f
scalarA name f fld@(Field _ _ args []) = withField name (errWrap $ f args) fld
:: (MonadPlus m, Aeson.ToJSON a)
=> Name -> (Arguments -> m a) -> Resolver m
scalarA name f fld@(Field _ _ args []) = withField name (lift $ f args) fld
scalarA _ _ _ = empty
array :: Alternative f => Name -> [Resolvers f] -> Resolver f
array :: MonadPlus m => Name -> [Resolvers m] -> Resolver m
array name resolvers = arrayA name $ \case
[] -> resolvers
_ -> empty
-- | Like 'array' but also taking 'Argument's.
arrayA
:: Alternative f
=> T.Text -> (Arguments -> [Resolvers f]) -> Resolver f
:: MonadPlus m
=> Name -> (Arguments -> [Resolvers m]) -> Resolver m
arrayA name f fld@(Field _ _ args sels) =
withField name (joinErrs $ traverse (`resolve` sels) $ f args) fld
withField name (traverse (`resolve` sels) $ f args) fld
-- | Like 'object'' but taking lists of 'Resolver's instead of a single list.
array' :: (Alternative f, Monad f) => T.Text -> f [[Resolver f]] -> Resolver f
array' :: MonadPlus m => Name -> m [Resolvers m] -> Resolver m
array' name resolvs = arrayA' name $ \case
[] -> resolvs
_ -> empty
-- | Like 'array'' but also taking 'Argument's.
arrayA'
:: (Alternative f, Monad f)
=> T.Text -> ([Argument] -> f [[Resolver f]]) -> Resolver f
:: MonadPlus m
=> Name -> (Arguments -> m [Resolvers m]) -> Resolver m
arrayA' name f fld@(Field _ _ args sels) = do
resolvs <- f args
withField name (joinErrs $ traverse (`resolve` sels) resolvs) fld
resolvs <- lift $ f args
withField name (traverse (`resolve` sels) resolvs) 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 => T.Text -> f [T.Text] -> Resolver f
enum :: MonadPlus m => Name -> m [T.Text] -> Resolver m
enum name enums = enumA name $ \case
[] -> enums
_ -> empty
-- | Like 'enum' but also taking 'Argument's.
enumA :: Alternative f => T.Text -> ([Argument] -> f [T.Text]) -> Resolver f
enumA name f fld@(Field _ _ args []) = withField name (errWrap $ f args) fld
enumA :: MonadPlus m => Name -> (Arguments -> m [T.Text]) -> Resolver m
enumA name f fld@(Field _ _ args []) = withField name (lift $ f args) fld
enumA _ _ _ = empty
-- | Helper function to facilitate 'Argument' handling.
withField
:: (Alternative f, Aeson.ToJSON a)
=> Name -> CollectErrsT f a -> Field -> CollectErrsT f (HashMap T.Text Aeson.Value)
withField :: (MonadPlus m, Aeson.ToJSON a)
=> Name -> CollectErrsT m a -> Field -> CollectErrsT m (HashMap T.Text Aeson.Value)
withField name v (Field alias name' _ _)
| name == name' = fmap getValue v
| name == name' = do
collection <- HashMap.singleton aliasOrName . Aeson.toJSON <$> runAppendErrs v
errors <- get
if null errors
then return collection
-- TODO: Report error when Non-Nullable type for field argument.
else put [] >> return (HashMap.singleton aliasOrName Aeson.Null)
| otherwise = empty
where
aliasOrName = fromMaybe name alias
getValue (x, []) = (HashMap.singleton aliasOrName $ Aeson.toJSON x, [])
-- TODO: Report error when Non-Nullable type for field argument.
getValue (_, _) = (HashMap.singleton aliasOrName Aeson.Null, [])
-- | 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.
resolve :: Alternative f => Resolvers f -> Fields -> CollectErrsT f Aeson.Value
resolve :: MonadPlus m => Resolvers m -> Fields -> CollectErrsT m Aeson.Value
resolve resolvers =
fmap (first Aeson.toJSON . fold)
fmap (Aeson.toJSON . fold)
. traverse (\fld -> getAlt (foldMap (Alt . ($ fld)) resolvers) <|> 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 = fromMaybe name alias
errmsg (Field alias name _ _) = do
addErrMsg $ T.unwords ["field", name, "not resolved."]
return $ HashMap.singleton aliasOrName Aeson.Null
where
aliasOrName = fromMaybe name alias

6
graphql.cabal
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@ -1,10 +1,10 @@
cabal-version: 1.12
-- This file has been generated from package.yaml by hpack version 0.31.1.
-- This file has been generated from package.yaml by hpack version 0.31.2.
--
-- see: https://github.com/sol/hpack
--
-- hash: 06d3fa29e37864ef5e4254215c50d95942b4a33b0ea4f4d4c930a071fdcd2872
-- hash: aba9e6c1a0e250a7d0dbabbbdae5dceb119343f6acf06744da66677a487fcca6
name: graphql
version: 0.3
@ -57,6 +57,7 @@ library
, megaparsec
, scientific
, text
, transformers
, unordered-containers
default-language: Haskell2010
@ -81,5 +82,6 @@ test-suite tasty
, tasty
, tasty-hunit
, text
, transformers
, unordered-containers
default-language: Haskell2010

1
package.yaml
View File

@ -30,6 +30,7 @@ dependencies:
- base >= 4.7 && < 5
- megaparsec
- text
- transformers
- unordered-containers
library:

19
tests/Test/StarWars/Schema.hs
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@ -2,10 +2,15 @@
{-# LANGUAGE OverloadedStrings #-}
module Test.StarWars.Schema where
import Control.Applicative (Alternative, empty)
import Control.Applicative (Alternative(..))
import Control.Monad (MonadPlus)
import Data.List.NonEmpty (NonEmpty((:|)))
import Data.GraphQL.Schema (Schema, Resolver, Argument(..), Value(..))
import Data.GraphQL.Schema ( Schema
, Resolver
, Argument(..)
, Value(..)
)
import qualified Data.GraphQL.Schema as Schema
import Test.StarWars.Data
@ -13,10 +18,10 @@ import Test.StarWars.Data
-- * Schema
-- See https://github.com/graphql/graphql-js/blob/master/src/__tests__/starWarsSchema.js
schema :: Alternative f => Schema f
schema :: MonadPlus m => Schema m
schema = hero :| [human, droid]
hero :: Alternative f => Resolver f
hero :: MonadPlus m => Resolver m
hero = Schema.objectA "hero" $ \case
[] -> character artoo
[Argument "episode" (ValueInt n)] -> character . getHero $ fromIntegral n
@ -25,17 +30,17 @@ hero = Schema.objectA "hero" $ \case
[Argument "episode" (ValueEnum "JEDI" )] -> character $ getHero 6
_ -> empty
human :: Alternative f => Resolver f
human :: MonadPlus m => Resolver m
human = Schema.objectA "human" $ \case
[Argument "id" (ValueString i)] -> character =<< getHuman i
_ -> empty
droid :: Alternative f => Resolver f
droid :: MonadPlus m => Resolver m
droid = Schema.objectA "droid" $ \case
[Argument "id" (ValueString i)] -> character =<< getDroid i
_ -> empty
character :: Alternative f => Character -> [Resolver f]
character :: MonadPlus m => Character -> [Resolver m]
character char =
[ Schema.scalar "id" $ id_ char
, Schema.scalar "name" $ name char