cascade dispatch commands?

[mwieder]

Just throwing this out here for brainstorming...

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

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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

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on someCommand @pParameters
  do_some_work_here_with_pParameters
end someCommand

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

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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

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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.

[dunbarx]

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

[FourthWorld]

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.

[mwieder]

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

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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:

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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

[bogs]

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