warning message could be more helpful

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?

Trac metadata

Trac field	Value
Version	6.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown