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{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies #-}
module Ambiguity where
class C1 a b | b -> a
class (C1 a b) => C2 a b where
foo :: b -> b
data A = A
data B = B
instance C1 A B
instance C2 A B where foo = error "urk"
-- this is accepted by both 6.12.3 and 7
runFoo1 :: C2 a b => b -> b
runFoo1 = foo
-- this is accepted by 6.12.3, but not by 7
runFoo2 :: B -> B
runFoo2 = foo
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