forked from github/purescript-typeable
22 lines
777 B
Haskell
22 lines
777 B
Haskell
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module Data.Dynamic where
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import Data.Exists (Exists, mkExists, runExists)
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import Data.Function ((#))
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import Data.Functor (map)
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import Data.Leibniz (runLeibniz)
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import Data.Maybe (Maybe)
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import Data.Typeable (class Typeable, TypeRep, eqT, typeRep)
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-- | A `Dynamic` holds a value `a` in a context `t`
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-- | and forgets the type of `a`
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data Dynamic' t a = Dynamic' (TypeRep a) (t a)
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data Dynamic t = Dynamic (Exists (Dynamic' t))
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-- | Wrap a value into a dynamic
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dynamic :: forall t a. Typeable a => t a -> Dynamic t
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dynamic a = Dynamic (mkExists (Dynamic' typeRep a))
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-- | Extract a value from a dynamic
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unwrapDynamic :: forall t a. TypeRep a -> Dynamic t -> Maybe (t a)
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unwrapDynamic ta (Dynamic e) = e # runExists \(Dynamic' ti v) -> map (\w -> runLeibniz w v) (eqT ti ta)
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