[GUI] Setting properties of a widget.

[David Sankel]

--- Axel Simon <A.Simon@ukc.ac.uk> wrote:
> I assume everybody is on holiday,
> 
> just a mail to keep the discussion on the core
> functionality going. So far
> it seems that we would like the following features:
> 
> a) mandatory arguments

Can someone give me an example where mandatory
arguments are required for a GUI toolkit?  Right now,
I can't think of any attributes that couldn't have
reasonable defaults.

> b) read-only arguments

I'm assuming that these are things like getting a
button's pixel width and height, which are a function
of its contents.

> c) write-only arguments

I can't think of any widgets that could utilize this
in an elegant way.  Perhaps the callback list?

> d) setting a property and getting a result

This would be most useful for setting callbacks and
returning the removeHandler.  Is there any other place
where this would be useful?  Perhaps this is a special
case?

> Regarding the unregister callback issue, I thought
> of the following: Maybe
> we can have the set function just taking one
> argument:
> 
>  set button $ on click =: messageBox "hi there" 

since there is no character savings between the above
and

set button [on click =: messageBox "hi there"]

I would vote against it.  I would rather make onClickH
a seperate function that returns the unregister
function.

removeHandler <- onClickH button (messageBox "hi
there")

On another note, I want to point out the difference
between using onClick and "on click".  What are the
benefits of using the second, more verbose, form?  It
is, IMHO, more confusing that the other version.

David J. Sankel