open-witness-0.6: test/Object.hs

module Object where

import Data.Type.OpenWitness
import Data.Type.Witness

data Object s =
    forall a. MkObject (OpenWitness s a)
                       a

matchObject :: OpenWitness s b -> Object s -> Maybe b
matchObject uqb (MkObject uqa a) = do
    Refl <- testEquality uqa uqb
    return a

makeConversions :: OpenWitness s b -> (b -> Object s, Object s -> Maybe b)
makeConversions wit = (MkObject wit, matchObject wit)

getConversions :: OW s (b -> Object s, Object s -> Maybe b)
getConversions = do
    wit <- newOpenWitnessOW
    return (makeConversions wit)