[Haskell-cafe] Pattern Matching
daniel.is.fischer at web.de
Fri Nov 13 07:02:53 EST 2009
Am Freitag 13 November 2009 11:05:15 schrieb Andrew Coppin:
> Colin Paul Adams wrote:
> > If I had a dollar for every time I've written something like
> > Andrew> case msg of eVENT_QUIT -> ... eVENT_POST -> ...
> > Andrew> eVENT_RESIZE -> ...
> > Andrew> and spent an hour trying to figure out why the messages
> > Andrew> aren't being processed right... ;-)
> > So why aren't they?
> Because what I *should* have written is
> case msg of
> _ | msg == eVENT_QUIT -> ...
> | msg == eVENT_POST -> ...
> | msg == eVENT_RESIZE -> ...
> which is something quite different.
> (And, entertainingly, because the incorrect version is perfectly valid
> source code, no compiler errors or warnings...)
It yells "overlapping patterns" -- you do pass -Wall, don't you?
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