#5910: Holes with other constraints
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Reporter: xnyhps | Owner:
Type: feature request | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 7.5
Keywords: holes | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: Incorrect warning at
compile-time
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by spl):
It seems to me that ambiguous types are the key problem here. We've been
working on this a bit at UHac, but we haven't yet reached a solution.
Thijs has already mentioned the problem with:
{{{
show _?x
}}}
Paolo has also pointed out the following:
{{{
data Foo a = Foo a
data Bar1 = Bar1
data Bar2 = Bar2
instance Show (Foo Bar1) where
instance Show (Foo Bar2) where
test = show (Foo _?y)
}}}
What type do we get for the type of {{{_?y}}}? It appears unknowable.
Perhaps we can solve only part of the problem.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5910#comment:9>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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