blob: 7ea0520133180669132d3a20c14f264c3fc8d0f0 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
|
{-# 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])
-}
|