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@int-index

int-index/polyconstraints-exercise.hs

Last active May 31, 2017 11:07
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Polyconstraints Exercise: @int-index solution
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polyconstraints-exercise.hs
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances,
TypeOperators, UndecidableInstances #-}
{-# LANGUAGE RankNTypes, ScopedTypeVariables, ConstraintKinds #-}
import Data.Constraint
import Data.Constraint.Forall
class C1 a b
class C2 a b
instance C1 a b => C2 a b
entl :: forall a . (Forall (C1 a)) :- (Forall (C2 a))
entl = Sub (forall (case inst :: forall b . Forall (C1 a) :- C1 a b of
Sub (Dict :: Dict (C1 a b)) -> Dict :: Dict (C2 a b)))
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