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Diffstat (limited to 'Data/GraphQL/Schema.hs')
| -rw-r--r-- | Data/GraphQL/Schema.hs | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/Data/GraphQL/Schema.hs b/Data/GraphQL/Schema.hs index 345984c..0a30eb9 100644 --- a/Data/GraphQL/Schema.hs +++ b/Data/GraphQL/Schema.hs @@ -1,6 +1,9 @@ {-# LANGUAGE CPP #-} {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE LambdaCase #-} +-- | This module provides the type Schema, +-- representing a GraphQL schema, and functions for defining +-- a schema. module Data.GraphQL.Schema ( Schema(..) , Resolver @@ -44,54 +47,70 @@ import Control.Arrow import Data.GraphQL.AST import Data.GraphQL.Error +-- | Schema represents a GraphQL schema. +-- f usually has to be an instance of Alternative. data Schema f = Schema [Resolver f] +-- | Resolver resolves a field in to a wrapped Aeson.Object with error information +-- (or empty). The wrapped f usually has to be an instance of Alternative. type Resolver f = Field -> CollectErrsT f Aeson.Object +-- | Subs represents a substitution. type Subs = Text -> Maybe Text +-- | Objects represent a list of named fields, each of which +-- yield a value of a specific type. object :: Alternative f => Text -> [Resolver f] -> Resolver f object name resolvs = objectA name $ \case [] -> resolvs _ -> empty +-- | Fields can accept arguments to further specify the return value. 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 +-- | Arguments can be used to further specify a scalar's return value. scalarA :: (Alternative f, Aeson.ToJSON a) => Text -> ([Argument] -> f a) -> Resolver f scalarA name f fld@(Field _ _ args _ []) = withField name (errWrap $ f args) fld scalarA _ _ _ = empty +-- | Arrays are like objects but have an array of resolvers instead of a list. array :: Alternative f => Text -> [[Resolver f]] -> Resolver f array name resolvs = arrayA name $ \case [] -> resolvs _ -> empty +-- | Arguments can be used to further specify an array's return values. arrayA :: Alternative f => Text -> ([Argument] -> [[Resolver f]]) -> Resolver f arrayA name f fld@(Field _ _ args _ sels) = withField name (joinErrs $ traverse (flip resolvers $ fields sels) $ f args) fld +-- | An enum 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 +-- | Arguments can be used to further specify an enum's return values. enumA :: Alternative f => Text -> ([Argument] -> f [Text]) -> Resolver f enumA name f fld@(Field _ _ args _ []) = withField name (errWrap $ f args) fld enumA _ _ _ = empty +-- | Used to implement a resolver with arguments. withField :: (Alternative f, Aeson.ToJSON a) => Text -> CollectErrsT f a -> Field -> CollectErrsT f (HashMap Text Aeson.Value) @@ -102,6 +121,9 @@ withField name f (Field alias name' _ _ _) = where aliasOrName = if T.null alias then name' else alias +-- | resolvers takes a list of resolvers and a list of fields, +-- 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 (first Aeson.toJSON . fold) @@ -111,10 +133,13 @@ resolvers resolvs = 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 fields contained in the given selection set. fields :: SelectionSet -> [Field] fields = catMaybes . fmap field |