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{-# OPTIONS_GHC -Wno-redundant-constraints -Wno-simplifiable-class-constraints #-}
{-# LANGUAGE
FlexibleContexts
, FlexibleInstances
, FunctionalDependencies
, MultiParamTypeClasses
, KindSignatures
, UndecidableInstances #-}
module T7875 where
import Data.Kind (Type)
class Het a b | a -> b where
het :: m (f c) -> a -> m b
class GHet (a :: Type -> Type) (b :: Type -> Type) | a -> b
instance GHet (K a) (K [a])
instance Het a b => GHet (K a) (K b)
data A a = A (A a)
data K x a = K x
instance Het (A a) (A [a]) where het = het1
het1 :: (GHet (K a) (K b)) => m (f c) -> a -> m b
-- Weird test case: (GHet (K a) (K b)) is simplifiable
het1 = undefined
{- Wanted
(GHet (K (A a)) (K (A [a])))
-- Fundeps give ([A a] ~ A [a])
-}
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