#1614: Type checker does not use fundep to avoid ambiguity
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Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 6.7
Severity: normal | Keywords:
Difficulty: Unknown | Os: MacOS X
Testcase: | Architecture: x86
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Compiling the following module gives an error
{{{
module X where
class C a | -> a
instance C Int
unC :: (C a) => a -> Int
unC i = undefined
test :: Int
test = unC undefined
}}}
Error message:
{{{
X.hs:13:7:
Ambiguous type variable `a' in the constraint:
`C a' arising from a use of `unC' at X.hs:13:7-19
Probable fix: add a type signature that fixes these type variable(s)
}}}
But that is just plain wrong. The functional dependency in the definition
of C forces a to be Int. No other type is possible. So what's ambiguous
about that?
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1614>
GHC <http://www.haskell.org/ghc/>
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