#3691: Error message doesn't mention necessary extension in warning
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Reporter: arsenm | Owner:
Type: bug | Status: closed
Priority: normal | Milestone:
Component: Compiler | Version: 6.10.4
Resolution: invalid | Keywords:
Difficulty: | Os:
Unknown/Multiple
Testcase: | Architecture:
Unknown/Multiple
Failure: Incorrect warning at compile-time |
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Comment (by simonpj):
Maybe I should change the resolution to "wontfix", then, because I have no
idea how to suggest the correct extension. I suppose GHC could warn you
if the behaviour might change if you added `ScopedTypeVariables`, and
suggest that you either add the flag, or use a different type variable
name. But that could result in hard-to-understand warnings about
perfectly reasonable Haskell 98 programs.
Example:
{{{
class C a where
op :: a -> a
op x = ....(foo :: a->a)....
}}}
This would provoke the warning, since the type signature for 'foo'
mentions 'a' which (were you to use `ScopedTypeVariables` would mean the
`a` in the class header.
Hmm. If people thing this is valuable, it would not be hard to implement.
If so, please re-open this ticket as a feature request.
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3691#comment:3>
GHC <http://www.haskell.org/ghc/>
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