#5858: type inference of an OverloadedString for a class instance with type
parameters
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Reporter: GregWeber | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.4.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by simonpj):
How's this? Instead of the old message
{{{
T5858.hs:11:7:
No instance for (InferOverloaded ([a0], [a1]))
arising from a use of `infer'
The type variables `a0', `a1' are ambiguous
Possible fix: add a type signature that fixes these type variable(s)
Possible fix:
add an instance declaration for (InferOverloaded ([a0], [a1]))
In the expression: infer ([], [])
In an equation for `foo': foo = infer ([], [])
}}}
we now get this:
{{{
T5858.hs:11:7:
Cannot resolve the instance for InferOverloaded ([a0], [a1])
arising from a use of `infer'
There is a potential instance available:
instance t1 ~ String => InferOverloaded (t1, t1)
-- Defined at T5858.hs:8:10
Possible fix: add a type signature to instantiate `a0, a1'
In the expression: infer ([], [])
In an equation for `foo': foo = infer ([], [])
}}}
Is that better?
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5858#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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