testsuite/tests/ghc-regress/indexed-types/should_compile/ind1.hs


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{-# LANGUAGE TypeFamilies #-}

-- Test type families

module ShouldCompile where

data family T a :: *

data instance T Bool = TBool !Bool

class C a where
  foo :: (a -> a) -> T a -> T a

instance C Bool where
  foo f (TBool x) = TBool $ f (not x)