56 lines
1.8 KiB
Haskell
56 lines
1.8 KiB
Haskell
-- | Definitions for @GraphQL@ input types.
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module Language.GraphQL.Type
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( Wrapping(..)
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) where
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import Data.Aeson as Aeson (ToJSON, toJSON)
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import qualified Data.Aeson as Aeson
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-- | GraphQL distinguishes between "wrapping" and "named" types. Each wrapping
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-- type can wrap other wrapping or named types. Wrapping types are lists and
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-- Non-Null types (named types are nullable by default).
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--
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-- This 'Wrapping' type doesn\'t reflect this distinction exactly but it is
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-- used in the resolvers to take into account that the returned value can be
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-- nullable or an (arbitrary nested) list.
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data Wrapping a
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= List [Wrapping a] -- ^ Arbitrary nested list
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| Named a -- ^ Named type without further wrapping
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| Null -- ^ Null
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deriving (Eq, Show)
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instance Functor Wrapping where
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fmap f (List list) = List $ fmap (fmap f) list
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fmap f (Named named) = Named $ f named
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fmap _ Null = Null
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instance Foldable Wrapping where
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foldr f acc (List list) = foldr (flip $ foldr f) acc list
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foldr f acc (Named named) = f named acc
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foldr _ acc Null = acc
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instance Traversable Wrapping where
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traverse f (List list) = List <$> traverse (traverse f) list
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traverse f (Named named) = Named <$> f named
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traverse _ Null = pure Null
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instance Applicative Wrapping where
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pure = Named
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Null <*> _ = Null
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_ <*> Null = Null
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(Named f) <*> (Named x) = Named $ f x
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(List fs) <*> (List xs) = List $ (<*>) <$> fs <*> xs
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(Named f) <*> list = f <$> list
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(List fs) <*> named = List $ (<*> named) <$> fs
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instance Monad Wrapping where
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return = pure
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Null >>= _ = Null
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(Named x) >>= f = f x
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(List xs) >>= f = List $ fmap (>>= f) xs
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instance ToJSON a => ToJSON (Wrapping a) where
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toJSON (List list) = toJSON list
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toJSON (Named named) = toJSON named
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toJSON Null = Aeson.Null
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