#3851: type family does not get expanded in ghc-6.12.1
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Reporter: kosmikus | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 6.12.1
Keywords: | Difficulty:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: GHC rejects valid
program
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Comment(by dreixel):
Note, however, that if we use a data family
{{{
data family DF a :: * -> *
data instance DF () a = D (App (Equ ()) a)
bar :: DF () () -> ()
bar (D (App Refl)) = ()
}}}
then both 6.10.4 and 6.12.1 fail to compile, and I wouldn't know how to
write this signature in any other way.
In any case, the example with type families makes the multirec library
basically unusable in 6.12. The workaround would require giving type
signatures which are easily 10 lines long. Is there a milestone for the
implementation of the new type-inference machinery?
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3851#comment:2>
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