Return "Perplexed"

Question

No matter what resources I study regarding AppleScript’s idle handler I return perplexed. I'm suspicious that my preconceptions may be the culprit.
Two aspects stand out:
1) In stark contrast to HyperTalk, it seems that AppleScript does not send itself idle messages — so perhaps the idle handler’s purpose is distinct from it typical HyperTalk use — and it’s unclear to me what mechanism, if any, continues to call the idle handler. Does a call to idle set up a process which can later be dismissed?
2) The Return statement of an “on idle” seems to perform a function distinctly different than the Return statements of other handlers ... as if it's actually is a different statement in disguise. It seems to specify, not a value that get returned, but the length of time to wait before the idle handler next executes.
Another question. Is it possible to invoke an “on idle” handler in a normal script. I get the feeling AppleScript needs to be in some sort of run state ...
Obviously I’m not clear on the concept, and even Matt Neuber’s book hasn't helped me.
Here's a failed example which I've treid to run in Script Editor:
property a : 0
on idle
set a to a + 1
return 1 -- should give result every second to the Result pane
-- should
end idle
-- in this example I call the idle handler
property a : 0
idle
on idle
set a to a + 1
return 1 -- should give a result every second to the Result pane
end idle
-- result: 1

Answer 1

>In stark contrast to HyperTalk, it seems that AppleScript does not send itself idle messages
That's correct. There is no automatic ide handling. To be honest it's been so long since I've used HyperTalk I don't remember how it works there, but I know they don't directly translate.
> The Return statement of an “on idle” seems to perform a function distinctly different than the Return statements of other handlers ... as if it's actually is a different statement in disguise. It seems to specify, not a value that get returned, but the length of time to wait before the idle handler next executes
That is exactly what it does - it tells AppleScript how long to wait before calling the idle handler again. This is documented in the AppleScript Language Guide section about idle handlers.
>Another question. Is it possible to invoke an “on idle” handler in a normal script. I get the feeling AppleScript needs to be in some sort of run state ...
The script does need to be saved as a 'stay-open' script in order for the idle handler to work.
>on idle
set a to a + 1
return 1 -- should give result every second to the Result pane
-- should
end idle
Contrary to your expectation, the return 1 statement does not return '1' to the result pane. It tells AppleScript to come back in 1 second and run the idle handler again.
Try:
<pre class=command>on idle
set a to a + 1
log a --> writes out the current value of a
return 1 --> come back again in 1 second
end idle</pre>