#1123: Impredicativity bug: forall not hoisted properly
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Reporter: Ashley Yakeley <[EMAIL PROTECTED]> | Owner: simonpj
Type: bug | Status: new
Priority: normal | Milestone: 6.10 branch
Component: Compiler | Version: 6.6
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Changes (by guest):
* cc: [EMAIL PROTECTED] (added)
Comment:
I believe I've run into this same bug with a simpler test case. runA2 is
the one that I've prefer to be able to write but am unable to.
{{{
data A s = A { unA :: () }
runA1 :: (forall s. A s) -> ()
runA1 a = unA a
-- doesn't work :(
runA2 :: (forall s. A s) -> ()
runA2 (A a) = a
runA3 :: (forall s. A s) -> ()
runA3 a = case a of A x -> x
runA4 :: (forall s. A s) -> ()
runA4 a = let A x = a in x
runA5 :: (forall s. A s) -> ()
runA5 a = go a
where go (A a) = a
}}}
The following error is generated by GHC 6.8.3
{{{
Couldn't match expected type `forall s. A s'
against inferred type `A s'
In the pattern: A a
In the definition of `runA2': runA2 (A a) = a
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1123#comment:7>
GHC <http://www.haskell.org/ghc/>
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