[mercury-users] GUI Toolkits and Mercury

[Julien Fischer]

On Wed, 23 Nov 2005, Jonathan Morgan wrote:

> > Some of the problems with existing GUIs are
> > - they are strongly imperative in nature;
> > - they do not enforce separation of application and user interface;
> > - they are invariably call-back based, which places control entirely
> >   with the GUI (not good);
> > - because everything is event driven and each event is potentially of
> >   interest to a large number of callbacks (about which the GUI engine
> >   knows nothing) a vast amount of time is wasted passing useless event
> >   messages back and forth and triggering callbacks that do nothing.
>
> So how would you improve that, since I think all modern GUIs are call-back
> based?  Anything built on them would have to be call-back based at some
> level.
>

Handling callbacks in Mercury bindings for such libraries is a real pain
in the neck in most cases as they generally force you hide program state
in all sorts of odd places (in the I/O state or in mutable variables).
How bad this is depends on the structure of the callback functions - the
GLUT binding and its associated examples in the extras distribution are
an example of a particularly restrictive callback structure.

Cheers,
Julien.
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