LiveCode Forums.

Posted: **Tue Mar 12, 2019 10:52 pm**

Just throwing this out here for brainstorming...

I have a need to cascade dispatch commands. What I've got is of the form

Code: Select all

dispatch "someCommand" to me with someParameters
if it is not "handled" then
  do_default_stuff
  -- otherwise the someCommand has done its work
end if

so if there is no "someCommand" in the message path code will be executed. On the other hand, if there is a "someCommand" handler in the message path (probably because of an added front- or backscript) then that code will be executed in place of the original callers default code. This works as designed. I'm happy.

The problem comes about if I want to extend that further, i.e., in a backscript I might have

Code: Select all

on someCommand @pParameters
  do_some_work_here_with_pParameters
end someCommand

and I want to give the ability to add more things later:

Code: Select all

on someCommand @pParameters
  do_some_work_here_with_pParameters
  dispatch "someCommand" to me with pParameters
end someCommand

That doesn't work because it just recurses into itself again. And

Code: Select all

on someCommand @pParameters
  do_some_work_here_with_pParameters
  pass "someCommand" to me with pParameters
end someCommand

also doesn't work for a similar reason, but only once around.

So anyone got ideas on how to cascade dispatch commands, whether or not they're found in the message path? I've got a solution that works in one specific use case, but it's too ugly to put in the margins here.

Posted: **Tue Mar 12, 2019 11:09 pm**

I've got a solution that works in one specific use case, but it's too ugly to put in the margins here.

Before we get into dispatching, do you know who Pierre de Fermat was? I think you do.

Craig Newman

Posted: **Wed Mar 13, 2019 12:43 am**

mwieder wrote: ↑
Tue Mar 12, 2019 10:52 pm
I've got a solution that works in one specific use case, but it's too ugly to put in the margins here.

He may have an ugly workaround, but the use case is pretty awesome. He demoed it at our local LiveCode meetup last week, and when he's ready to show it I know a number of people who will be all over it.

Posted: **Sat Apr 06, 2019 1:01 am**

OK - it turns out that dispatch commands *do* cascade properly... the problem is in the script editor itself.

I didn't read the documentation carefully enough to realize the the "it" value returned from a dispatch command can have one of three (!) values:

handled
unhandled
passed

so the script editor (or any other code) that simply checks to see if a dispatch command has been handled

Code: Select all

dispatch "someCommand"
if it is not "handled" then
-- do something here if there was no "someCommand" in the message path
end if

will only catch one of the three values and fail if it is passed. It really should read:

Code: Select all

dispatch "someCommand"
if it is "unhandled" then
-- do something here if there was no "someCommand" in the message path
end if

Now filed as bug report #21899
https://quality.livecode.com/show_bug.cgi?id=21899

Posted: **Sat Apr 06, 2019 10:56 am**

Looking at this kind of thing, I can see just how far I still have to go. I'd never have caught it.

LiveCode Forums.

cascade dispatch commands?

cascade dispatch commands?

Re: cascade dispatch commands?

Re: cascade dispatch commands?

Re: cascade dispatch commands?

Re: cascade dispatch commands?