#1347: warning message could be more helpful
-----------------------+----------------------------------------------------
Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.6.1
Severity: normal | Keywords:
Difficulty: Unknown | Os: Unknown
Testcase: | Architecture: Unknown
-----------------------+----------------------------------------------------
Code was:
{{{
case msg of
wM_DESTROY -> do
sendMessage hwnd wM_QUIT 1 0
return 0
otherwise -> defWindowProc (Just hwnd) msg wparam lparam
}}}
warning message was:
{{{
Warning: Pattern match(es) are overlapped
In a case alternative: otherwise -> ...
}}}
It took me a long time to realize that wM_DESTROY was being interpreted as
a new variable name shadowing the imported constant. The compiler
realizes that something is probably wrong (overlapped patterns). It could
further check and see that wM_DESTROY is shadowing an already existing
binding and give a messages like this:
{{{
Warning: Pattern match(es) are overlapped
In a case alternative: otherwise -> ...
Hint: Are you sure you want to shadow the existing binding for
wM_DESTROY?
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1347>
GHC <http://www.haskell.org/ghc/>
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