#5340: wrong warning on incomplete case analysis in conjunction with empty data
declarations
---------------------------------+------------------------------------------
Reporter: Lemming | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.12.3 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
---------------------------------+------------------------------------------
I load the following code into GHCi with warnings enabled (-Wall)
{{{
{-# LANGUAGE EmptyDataDecls #-}
data Empty
data EitherStrict a b = LeftStrict !a | RightStrict !b
test :: Char
test =
case undefined :: EitherStrict Empty Char of
-- LeftStrict _ -> undefined
RightStrict b -> b
}}}
I get the warning:
{{{
CaseOfEmptyData.hs:9:3:
Warning: Pattern match(es) are non-exhaustive
In a case alternative: Patterns not matched: LeftStrict _
}}}
I think this warning is wrong, since the LeftStrict case cannot happen. Am
I right?
This may be related to #2431.
This problem is of minor priority for me. I found that in the original
problem EmptyDataDecls would not helped me at all, and I found a better
solution in this particular case.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5340>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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