Alex Tweedly wrote:
You need to be careful (i.e. precise) when you say that :-)
send "xxx" to me in N ticks
is kind of like a (delayed) goto - the message is queues, then the
code following the 'send'; statement is executed (so it's not really
quite like a GOTO), and when the handler (and any calling handlers)
exits, or a "wait with messages or other 'send in time' statement is
executed) then the message queue will send the message
On the other hand,
send "xxx" to me
is just not at all like a GOTO. The handler is executed immediately
(via the message passing), but THEN the following code is also
executed - so it's very like a GOSUB, and therefore very, very like
just using the handler name directly; basically the only difference
seems to be that it's less efficient.
So if you were doing simply 'send "xxx" to me' then you would still be
building up a stack of calls; we can argue semantics whether it is
officially called "recursion" or not - but the effect would be that
all of these would have context that needs to be kept simultaneously.
Hmmm - not easy to follow what I wrote there - try this concrete example
instead :
The following 3 code samples differ *only* in the recursive call / send
statement.
on subCheckNow
-- do stuff here
if lCounter > 3 then exit subCheckNow
add 1 to lCounter
put "before" & cr after field "F"
send "subCheckNow" to me
put "after" & cr after field "F"
end subCheckNow
and ALSO
on subCheckNow
-- do stuff here
if lCounter > 3 then exit subCheckNow
add 1 to lCounter
put "before" & cr after field "F"
subCheckNow
put "after" & cr after field "F"
end subCheckNow
BOTH produce
before
before
before
before
after
after
after
after
But in contrast,
on subCheckNow
-- do stuff here
if lCounter > 3 then exit subCheckNow
add 1 to lCounter
put "before" & cr after field "F"
send "subCheckNow" to me in 1 tick
put "after" & cr after field "F"
end subCheckNow
produces
before
after
before
after
before
after
before
after
--
Alex Tweedly http://www.tweedly.net
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