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47 lines
1.4 KiB
Haskell
47 lines
1.4 KiB
Haskell
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-- | The 'WithOptional' Functor and associated operations.
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module Hasura.RQL.DDL.Webhook.Transform.WithOptional
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( WithOptional (..),
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withOptional,
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)
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where
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-------------------------------------------------------------------------------
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import Data.Aeson (FromJSON, ToJSON)
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import Data.Coerce (Coercible)
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import Hasura.Prelude
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-------------------------------------------------------------------------------
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-- | Enrich a 'Functor' @f@ with optionality; this is primarily useful when
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-- one wants to annotate fields as optional when using the Higher-Kinded Data
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-- pattern.
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--
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-- 'WithOptional'@ f@ is equivalent to @Compose Maybe f@.
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newtype WithOptional f result = WithOptional
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{ getOptional :: Maybe (f result)
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}
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deriving stock (Eq, Functor, Foldable, Generic, Show)
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deriving newtype (FromJSON, ToJSON)
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deriving newtype instance
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(NFData (f result)) =>
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NFData (WithOptional f result)
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-- | 'WithOptional' smart constructor for the special case of optional values
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-- that are representationally equivalent to some "wrapper" type.
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--
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-- For example:
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-- @
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-- withOptional \@HeaderTransformsAction headers == WithOptional $ fmap HeadersTransform headers
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-- @
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--
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-- In other words: this function observes the isomorphism between @'Maybe' a@
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-- and @'WithOptional' f b@ if an isomorphism exists between @a@ and @f b@.
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withOptional ::
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forall a b f.
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Coercible a (f b) =>
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Maybe a ->
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WithOptional f b
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withOptional = coerce
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