Constrain the resolvers with MonadIO
This replaces the most usages of MonadPlus, which is not appropriate for the resolvers, since a resolver is unambiguously chosen by the name (no need for 'mplus'), and the resolvers are often doing IO.
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@ -1,9 +1,10 @@
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{-# LANGUAGE OverloadedStrings #-}
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-- | This module provides the function to execute a @GraphQL@ request --
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-- according to a 'Schema'.
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module Language.GraphQL.Execute (execute) where
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import Control.Monad (MonadPlus(..))
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import Control.Monad.IO.Class (MonadIO)
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import qualified Data.List.NonEmpty as NE
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import Data.List.NonEmpty (NonEmpty((:|)))
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import qualified Data.Aeson as Aeson
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@ -21,17 +22,22 @@ import qualified Language.GraphQL.Schema as Schema
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-- Returns the result of the query against the 'Schema' wrapped in a /data/ field, or
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-- errors wrapped in an /errors/ field.
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execute
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:: (MonadPlus m)
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=> Schema m -> Schema.Subs -> AST.Document -> m Aeson.Value
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execute schema subs doc = do
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coreDocument <- maybe mzero pure (Transform.document subs doc)
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document schema coreDocument
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:: MonadIO m
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=> Schema m -> Schema.Subs -> AST.Document -> m Aeson.Value
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execute schema subs doc =
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maybe transformError (document schema) $ Transform.document subs doc
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where
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transformError = return $ Aeson.object
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[("errors", Aeson.toJSON
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[ Aeson.object [("message", "Schema transformation error.")]
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]
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)]
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document :: MonadPlus m => Schema m -> AST.Core.Document -> m Aeson.Value
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document :: MonadIO m => Schema m -> AST.Core.Document -> m Aeson.Value
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document schema (op :| []) = operation schema op
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document _ _ = error "Multiple operations not supported yet"
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operation :: MonadPlus m => Schema m -> AST.Core.Operation -> m Aeson.Value
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operation :: MonadIO m => Schema m -> AST.Core.Operation -> m Aeson.Value
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operation schema (AST.Core.Query flds)
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= runCollectErrs (Schema.resolve (NE.toList schema) (NE.toList flds))
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operation schema (AST.Core.Mutation flds)
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@ -25,7 +25,7 @@ module Language.GraphQL.Schema
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, Value(..)
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) where
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import Control.Monad (MonadPlus(..))
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import Control.Monad.IO.Class (MonadIO(..))
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import Control.Monad.Trans.Class (lift)
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import Control.Monad.Trans.Except (runExceptT)
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import Data.Foldable ( find
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@ -44,11 +44,11 @@ import Language.GraphQL.Type
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import Language.GraphQL.AST.Core
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-- | A GraphQL schema.
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-- @f@ is usually expected to be an instance of 'Alternative'.
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-- @m@ is usually expected to be an instance of 'MonadIO'.
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type Schema m = NonEmpty (Resolver m)
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-- | Resolves a 'Field' into an @Aeson.@'Aeson.Object' with error information
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-- (or 'empty'). @m@ is usually expected to be an instance of 'MonadPlus'.
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-- (or 'empty'). @m@ is usually expected to be an instance of 'MonadIO.
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data Resolver m = Resolver
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Text -- ^ Name
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(Field -> CollectErrsT m Aeson.Object) -- ^ Resolver
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@ -61,18 +61,18 @@ type Arguments = [Argument]
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type Subs = Name -> Maybe Value
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-- | Create a new 'Resolver' with the given 'Name' from the given 'Resolver's.
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object :: MonadPlus m => Name -> ActionT m [Resolver m] -> Resolver m
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object :: MonadIO m => Name -> ActionT m [Resolver m] -> Resolver m
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object name = objectA name . const
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-- | Like 'object' but also taking 'Argument's.
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objectA :: MonadPlus m
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objectA :: MonadIO m
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=> Name -> (Arguments -> ActionT m [Resolver m]) -> Resolver m
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objectA name f = Resolver name $ resolveFieldValue f resolveRight
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where
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resolveRight fld@(Field _ _ _ flds) resolver = withField (resolve resolver flds) fld
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-- | Like 'object' but also taking 'Argument's and can be null or a list of objects.
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wrappedObjectA :: MonadPlus m
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wrappedObjectA :: MonadIO m
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=> Name -> (Arguments -> ActionT m (Wrapping [Resolver m])) -> Resolver m
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wrappedObjectA name f = Resolver name $ resolveFieldValue f resolveRight
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where
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@ -80,23 +80,23 @@ wrappedObjectA name f = Resolver name $ resolveFieldValue f resolveRight
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= withField (traverse (`resolve` sels) resolver) fld
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-- | Like 'object' but can be null or a list of objects.
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wrappedObject :: MonadPlus m
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wrappedObject :: MonadIO m
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=> Name -> ActionT m (Wrapping [Resolver m]) -> Resolver m
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wrappedObject name = wrappedObjectA name . const
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-- | A scalar represents a primitive value, like a string or an integer.
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scalar :: (MonadPlus m, Aeson.ToJSON a) => Name -> ActionT m a -> Resolver m
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scalar :: (MonadIO m, Aeson.ToJSON a) => Name -> ActionT m a -> Resolver m
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scalar name = scalarA name . const
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-- | Like 'scalar' but also taking 'Argument's.
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scalarA :: (MonadPlus m, Aeson.ToJSON a)
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scalarA :: (MonadIO m, Aeson.ToJSON a)
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=> Name -> (Arguments -> ActionT m a) -> Resolver m
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scalarA name f = Resolver name $ resolveFieldValue f resolveRight
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where
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resolveRight fld result = withField (return result) fld
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-- | Lika 'scalar' but also taking 'Argument's and can be null or a list of scalars.
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wrappedScalarA :: (MonadPlus m, Aeson.ToJSON a)
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wrappedScalarA :: (MonadIO m, Aeson.ToJSON a)
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=> Name -> (Arguments -> ActionT m (Wrapping a)) -> Resolver m
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wrappedScalarA name f = Resolver name $ resolveFieldValue f resolveRight
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where
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@ -106,23 +106,23 @@ wrappedScalarA name f = Resolver name $ resolveFieldValue f resolveRight
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resolveRight fld (List result) = withField (return result) fld
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-- | Like 'scalar' but can be null or a list of scalars.
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wrappedScalar :: (MonadPlus m, Aeson.ToJSON a)
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wrappedScalar :: (MonadIO m, Aeson.ToJSON a)
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=> Name -> ActionT m (Wrapping a) -> Resolver m
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wrappedScalar name = wrappedScalarA name . const
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-- | Represents one of a finite set of possible values.
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-- Used in place of a 'scalar' when the possible responses are easily enumerable.
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enum :: MonadPlus m => Name -> ActionT m [Text] -> Resolver m
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enum :: MonadIO m => Name -> ActionT m [Text] -> Resolver m
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enum name = enumA name . const
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-- | Like 'enum' but also taking 'Argument's.
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enumA :: MonadPlus m => Name -> (Arguments -> ActionT m [Text]) -> Resolver m
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enumA :: MonadIO m => Name -> (Arguments -> ActionT m [Text]) -> Resolver m
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enumA name f = Resolver name $ resolveFieldValue f resolveRight
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where
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resolveRight fld resolver = withField (return resolver) fld
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-- | Like 'enum' but also taking 'Argument's and can be null or a list of enums.
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wrappedEnumA :: MonadPlus m
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wrappedEnumA :: MonadIO m
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=> Name -> (Arguments -> ActionT m (Wrapping [Text])) -> Resolver m
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wrappedEnumA name f = Resolver name $ resolveFieldValue f resolveRight
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where
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@ -132,10 +132,10 @@ wrappedEnumA name f = Resolver name $ resolveFieldValue f resolveRight
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resolveRight fld (List resolver) = withField (return resolver) fld
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-- | Like 'enum' but can be null or a list of enums.
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wrappedEnum :: MonadPlus m => Name -> ActionT m (Wrapping [Text]) -> Resolver m
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wrappedEnum :: MonadIO m => Name -> ActionT m (Wrapping [Text]) -> Resolver m
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wrappedEnum name = wrappedEnumA name . const
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resolveFieldValue :: MonadPlus m
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resolveFieldValue :: MonadIO m
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=> ([Argument] -> ActionT m a)
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-> (Field -> a -> CollectErrsT m (HashMap Text Aeson.Value))
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-> Field
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@ -149,7 +149,7 @@ resolveFieldValue f resolveRight fld@(Field _ _ args _) = do
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return $ HashMap.singleton (aliasOrName fld) Aeson.Null
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-- | Helper function to facilitate 'Argument' handling.
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withField :: (MonadPlus m, Aeson.ToJSON a)
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withField :: (MonadIO m, Aeson.ToJSON a)
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=> CollectErrsT m a -> Field -> CollectErrsT m (HashMap Text Aeson.Value)
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withField v fld
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= HashMap.singleton (aliasOrName fld) . Aeson.toJSON <$> runAppendErrs v
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@ -157,11 +157,11 @@ withField v fld
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-- | Takes a list of 'Resolver's and a list of 'Field's and applies each
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-- 'Resolver' to each 'Field'. Resolves into a value containing the
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-- resolved 'Field', or a null value and error information.
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resolve :: MonadPlus m
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resolve :: MonadIO m
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=> [Resolver m] -> Fields -> CollectErrsT m Aeson.Value
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resolve resolvers = fmap (Aeson.toJSON . fold) . traverse tryResolvers
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where
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tryResolvers fld = mplus (maybe mzero (tryResolver fld) $ find (compareResolvers fld) resolvers) $ errmsg fld
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tryResolvers fld = maybe (errmsg fld) (tryResolver fld) $ find (compareResolvers fld) resolvers
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compareResolvers (Field _ name _ _) (Resolver name' _) = name == name'
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tryResolver fld (Resolver _ resolver) = resolver fld
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errmsg fld@(Field _ name _ _) = do
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