#5821: SPECIALISE fails with a cryptic warning
---------------------------------+------------------------------------------
Reporter: rl | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 7.6.1
Component: Compiler | Version: 7.5
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: Incorrect warning at
compile-time
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by illissius):
Just to amuse matters further, these both work, with both 7.0 and 7.4:
{{{
foo :: (Num a, b ~ T a) => a -> b
{-# SPECIALISE foo :: b ~ Bool => Int -> b #-}
}}}
{{{
foo :: (Num a, b ~ T a) => a -> b
{-# SPECIALISE foo :: Int -> Bool #-}
}}}
that is, completely the opposite of the original example, now it works if
and only if I *do* expand the type family, and it doesn't matter what I do
with the equality constraint.
(FTR I'm testing with 7.0 and 7.4 because I don't have a 7.2 on hand.)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5821#comment:3>
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