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{-# LANGUAGE Haskell2010 #-}
{-# LANGUAGE GADTs, RoleAnnotations #-}
unit p where
signature H where
type role F phantom
data F a
module M where
import H
-- This will typecheck
f :: (F a ~ F b) => a -> b
f x = x
unit h where
module H where
-- But this is an invalid implementation of F
type F a = ()
unit r where
dependency p[H=h:H]
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