#2296: Functional dependencies error message has no position information
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Reporter: NeilMitchell | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.8.2
Severity: minor | Resolution:
Keywords: | Testcase:
Architecture: Unknown | Os: Unknown
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Comment (by NeilMitchell):
I just got a very similar error message off slightly different code, which
gives slightly different information:
{{{
E:\Neil\thesis\obj\haskell2/Proof_default.hs:1:0:
Couldn't match expected type `VarName' against inferred type `Expr'
Expected type: ([VarName], [Expr])
Inferred type: ([Expr], [b])
When using functional dependencies to combine
Subst (Sat a) ([a], [b]) (Sat b),
arising from the instance declaration at
E:\Neil\thesis\obj\haskell2/Pr
of_default.hs:140:0
Subst (Sat Expr) ([VarName], [Expr]) (Sat Expr),
arising from a use of `/'
at
E:\Neil\thesis\obj\haskell2/Proof_default.hs:402:17-43
}}}
Here the relevant position is the second one (the use, not the
definition), so this bug can't just be fixed by grabbing the first
position out of the list. I've again attached a sample piece of code.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2296#comment:1>
GHC <http://www.haskell.org/ghc/>
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