#5655: Oddity with ConstraintKinds and TypeFamilies
-------------------------------+--------------------------------------------
Reporter: illissius | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 7.3 | Keywords:
Testcase: | Blockedby:
Os: Linux | Blocking:
Architecture: x86_64 (amd64) | Failure: GHC rejects valid program
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See the attached program (not sure how to reduce it further - I don't know
whether the relevant interaction is really with !TypeFamilies, Rank2Types,
or what).
When compiled with -DWORKAROUND, it compiles, when without, it doesn't.
The difference:
{{{
#ifndef WORKAROUND
ap :: (forall a. C e a => a -> r) -> e -> r
#else
ap :: c ~ C e => (forall a. c a => a -> r) -> e -> r
#endif
}}}
(Where 'C e' is an associated type of 'e' of kind * -> Constraint.)
I sort of assumed that 'Some Type' and 'a ~ Some Type => a' would always
be equivalent, but maybe I'm wrong. Feel free to mark as invalid if I am.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5655>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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