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{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies,
FlexibleInstances, UndecidableInstances #-}
-- UndecidableInstances now needed because the Coverage Condition fails
-- !!! Functional dependencies
-- This one gave another fail in tcReadMutVar
module M1 where
class HasFoo a foo | a -> foo where
foo :: a -> foo
instance HasFoo Int Int where
foo = id
instance HasFoo a b => HasFoo [a] b where
foo = foo . head
test:: [[Int]] -> Int
test = foo
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