RE: [wxhaskell-users] setting callbacks in callbacks

[Daan L. <daa...@xs...>]

> -----Original Message-----
> by David Roundy
>
> The following code gives me "interesting" results:
> 
> module Main where
> import Graphics.UI.WX
> 
> main = start $ do f <- frame [text := "layout demo"]
>                   h <- staticText f []
>                   hello h
>                   q <- button f [text := "quit", on command 
> := close f]
>                   set f [layout := column 5 [widget h,
>                                              widget q]] 
> 
> hello st = set st [text := "Hello world!",
>                    on click := \_ -> goodbye st]
> goodbye st = set st [text := "Goodbye world!",
>                      on click := \_ -> hello st]
> 
> [snip]
> 
> So my question is, am I supposed to be allowed to modify a 
> callback function within that callback function? 


I have found the bug. It is in my implementation of "event filters". 
There is just one primitive event, "mouse" that
gets all mouse events. For convenience there is a host of "event
filters"
on top of "mouse". Somehow, I made a mistake in their implementation
and I will try to fix it in the next release. Note that your problem
goes away when you use the basic "mouse" events.

-- Daan.



> Obviously I 
> could get the same functionality either using an IORef or by 
> checking the current contents of the text, but I don't see 
> why you shouldn't be able to modify a callback within the 
> callback.  Or perhaps there is some other more subtle problem 
> going on here...
> -- 
> David Roundy
> http://www.abridgegame.org
> 
> 
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