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{-# OPTIONS_GHC -ddump-types #-}
{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies #-}
-- See Trac #1456
-- The key thing here is that foo should get the type
-- foo :: forall b s t1. (Zork s (Z [Char]) b)
-- => Q s (Z [Char]) t1 -> ST s ()
-- Note the quantification over 'b', which was previously
-- omitted; see Note [Important subtlety in oclose] in FunDeps
module ShouldCompile where
import GHC.ST
data Q s a chain = Node s a chain
data Z a = Z a
s :: Q t (Z [Char]) t1 -> Q t (Z [Char]) t1
s = undefined
class Zork s a b | a -> b where
huh :: Q s a chain -> ST s ()
foo b = huh (s b)
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