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From: edp@jareth.enet.dec.com (Eric Postpischil (Always mount a scratch monkey.))
Newsgroups: comp.sys.handhelds
Subject: Re: Using CLEAR in progs (Was: Re: new puzzle, new blinky)
Keywords: 48sx, CLEAR, programs
Message-ID: <19504@shlump.nac.dec.com>
Date: 28 Jan 91 13:57:55 GMT
References: <1991Jan26.221145.29164@portia.Stanford.EDU> <25590090@hpcvra.cv.hp.com.> <56027@eerie.acsu.Buffalo.EDU> <19462@shlump.nac.dec.com>
Sender: newsdaemon@shlump.nac.dec.com
Reply-To: edp@jareth.enet.dec.com (Eric Postpischil (Always mount a scratch monkey.))
Organization: Digital Equipment Corporation
Lines: 19

It has been pointed out that saving the stack is simple (DEPTH ->LIST -> local).
However, this method runs the risk of losing the entire stack should the program
terminate abnormally -- whether by internal error or the user pressing
on/attention.

Still, there are times when it is useful to restore the stack to a fixed point. 
For example, after running a clause in an IFERR statement, which can leave a
variable number of objects on the stack, depending upon where an error is
encountered or the setting of the last-arguments flag.  One person suggested a
clear-to-mark routine which scanned the stack looking for a particular argument.
However, this routine is slow and does not distinguish between marks left by
different invocations.  A simpler way to accomplish this is:  DEPTH ->
STACKLEVEL << program >>.  Anywhere in the program, the stack can be restored to
the initial point with DEPTH STACKLEVEL - DROPN.


				-- edp (Eric Postpischil)
				"Always mount a scratch monkey."
				edp@jareth.enet.dec.com