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From: bson@rice-chex.ai.mit.edu (Jan Brittenson)
Newsgroups: comp.sys.handhelds
Subject: Re: CLEAR-TO-MARK code
Message-ID: <13117@life.ai.mit.edu>
Date: 1 Feb 91 08:40:36 GMT
References: <C97F60BDE6FF20B17D@ISUVAX.BITNET>
Sender: news@ai.mit.edu
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In a posting of [29 Jan 91 05:30:00 GMT]
   TNAN0@CCVAX.IASTATE.EDU writes:

 > Ok, here's one peraino...
 >
 > << DO RAND UNTIL DUP .999 > END >>
 >
 > Assume all values are needed until completion of the program (let's
 > say they would be used in the event that the last value was exactly

I'm not sure exactly what I'm arguing and why, but hey...

   This wouldn't work, as you wouldn't have any idea how many random
numbers you had left on the stack. Not without a counter, in which
case you know how many to drop if you decide not to use them.

   To illustrate my point, assume that at the beginning the stack
looks like this - am I the only one to prefer the good ol' FIX 4? :-)


	3: "ABC"
	2: 0.1000
	1: 0.4711

   Further assume that after the loop above exits, the stack looks
like this:

	7: "ABC"
	6: 0.1000
	5: 0.4711
	4: 0.rand
	3: 0.rand
	2: 0.rand
	1: 0.9990

A counter is need, and one way is to keep it on top of the stack:

	<< 0 DO 1 + RAND SWAP UNTIL OVER .999 >= END >>

Thus you would be left with:

	8: "ABC"
	7: 0.1000
	6: 0.4711
	5: 0.rand
	4: 0.rand
	3: 0.rand
	2: 0.9990
	1: 4.0000

Then we're compatible with DROPN, ->ARR, ->LIST, etc.
You can also feed it to a program:

	<< -> Nelem
	   << 1 Nelem START
	        GOBBLE
	      NEXT
	   >>
	>>


   I'm not saying CLEAR is _never_ necessary... just that it sort of
defeats the purpose of a stack to clear it.

						-- Jan Brittenson
						   bson@ai.mit.edu

;; "Make sure the brain is connected before the mouth is started."