Am Freitag 17 April 2009 01:37:25 schrieb Tsunkiet Man:
> Hello,
>
> what you suggested worked! Im very happy with it. However another error
> suddenly came up. It sais the last statement in a 'do' must be an
> expression, he is refering to line 41:45
>
> I change my code to this:
>
> on (menu exit) := close f,
> on (menu open) := onOpen f dt vFile ]
>
> return ()
>
> where
> onOpen :: Frame a -> staticText c -> Var b -> IO ()
> onOpen frame stat var = do file <- fileOpenDialog frame
> False True "Open File" [("PGM bestanden (*.pgm)",["*.pgm"]),("Alle
> bestanden (*.*)",["*.*"])] "" ""
> case file of
> Nothing -> return ()
> Just file -> set stat [text
>
> := "HELLO"]
>
> return ()
In the "Just file" case, you want to have two IO-actions. If you don't use
(>>=) or (>>)
to chain them together, you must put them in a do-block, so
case file of
Nothing -> return ()
Just file -> do set stat [text := "HELLO"]
return ()
But I think you can omit the return () in that branch anyway, set foo bar
should have the
correct type already.
>
> As far as I can tell, if the file is nothing it will return something of IO
> () and if the file is something it will return something of IO (). So that
> error is kind of strange in my opinion. Do you know what caused it?
>
> Thanks for your help!
>
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