Setting properties of a widget.

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
b) read-only arguments
c) write-only arguments
d) setting a property and getting a result

I guess the general outline will be that of Daan's posting. 

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" 

so that we need to use a special mapSet for several properties

mapSet button [label =: "Open Dialogs", on click =: messageBox "hi there"]

This enables each property we set to return something as well. In case of 
attaching a callback, we could return the unregister function:

unReg <- set button $ on click =: messageBox "hi there"

What do you guys think?


Axel.