CLIM mail archive


presentation actions - how can I live without them?

>>If you think you want presentation actions, you are probably wrong.
>I am rather lost.
>We continue to develop a GUI substrate (called the Jin system) which
>provides a variety of buttons, switches, thumb wheels, dials, sliders
>etc. as the kernel of reusable utilities.
>All interaction is through the mouse.
>The logic of presentation actions seems to be appropriate.

In Symbolics mouse handling, which provided the basic ideas for CLIM
mouse handling, there's a distinction between presentation handlers
which translate objects into other objects (presentation translators)
and presentation handlers which immediately perform an action on an
object (presentation actions). In most circumstances, if you want a
mouse click on an object to perform some action on that object, you
should write a command (rather than a handler) that peforms the action
and then write a presentation-to-command-translator which will result
in an invocation of that command on the moused-upon object.
Presentation actions are only appropriate for a few special purposes,
though they're quite necessary for those purposes.

So it's not the idea of actions invoked by the mouse that's "probably
wrong" (an unfortunate choice of words in any case); it's the specific
use of presentation translators vs presentation actions. Also at issue
was whether CLIM should provide presentation actions at all, given
their limited appropriateness.




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