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{-# OPTIONS_GHC -fno-warn-redundant-constraints #-}
{-# LANGUAGE RankNTypes, MultiParamTypeClasses, FunctionalDependencies #-}
-- This one caught a bug in the implementation of functional
-- dependencies, where improvement must happen when
-- checking the call in 'test4'
module ShouldCompile where
newtype M s a = M a
class Modular s a | s -> a
wim :: forall a w. Integral a
=> a -> (forall s. Modular s a => M s w) -> w
wim i k = error "urk"
test4' :: (Modular s a, Integral a) => M s a
test4' = error "urk"
test4 = wim 4 test4'
-- Integral a0, (Modular s a0 => Modular s1 a1, Integral a1, M s1 a1 ~ M s w0)
-- Under the implication, [D] a1 ~ a0, [W] a1 ~ w0
-- Hence a1 := w0, [D] w0 ~ a0
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