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