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From: pozsvath@ctvax.UUCP
Newsgroups: net.ai
Subject: Re: Request for OPS5 examples - (nf)
Message-ID: <6361@uiucdcs.UUCP>
Date: Fri, 23-Mar-84 22:55:52 EST
Article-I.D.: uiucdcs.6361
Posted: Fri Mar 23 22:55:52 1984
Date-Received: Sun, 25-Mar-84 12:44:03 EST
Lines: 68

#R:dcdwest:-10800:ctvax:45200002:000:1807
ctvax!pozsvath    Mar 22 21:52:00 1984

;;;							  /
;;;						Peter Ozsvath
;;;	
;;;			Factorial Program in OPS-5
;;;		 Simulates the stack in working memory     
;;;	

;;;  Stage 1. Fill the working memory with (fact 1) (fact 2)...(fact n)
;;;	      
(p fact0 (fact {<x> = 0}) --> (remove 1) (make factorial 1 1))

(p factn (fact {<n> > 0}) --> (make fact (compute <n> - 1)))

;;;  Negative number entered. Quit
(p factneg (fact {<n> < 0}) -->
    (write "Good-bye."))

;;;  Stage 2. Sweep out the unnecessary (fact k) and (factorial k (k-1)!) 
;;;	and add new (factorial (k+1) k!
;;;	
(p factorial (factorial <x> <y>) (fact <x>) --> 
    (remove 2)
    (remove 1)
    (make factorial (compute (<x> + 1)) (compute (<x> * <y>))))

;;;  When no more (fact k) statements are left, factorial k is fount
;;;
(p factorial2 (factorial <x> <y>) -(fact <x>) -->
    (write (crlf))
    (write (compute <x> - 1))
    (write "!! =")
    (write <y>)
    (write (crlf))
    (make infinifact))

;;;  Called once at the beginning
;;;
(p pretty_fact (start) -->
    (write "Program to demonstrate the power, compactness, and robustness")
    (write (crlf))
    (write "of the Winning OPS 5. This program inputs numbers whose")
    (write (crlf))
    (write "factorials - lo and behold - it computes RECURSIVELY")
    (write (crlf))
    (write (crlf))
    (remove 1)
    (make infinifact))

;;;  Circular "loop" that reads in numbers
;;;
(p infinifact (infinifact) -->
    (remove 1)
    (write "Enter a positive number to compute its factorial,")
    (write (crlf))
    (write "or a negative one to quit")
    (write (crlf))
    (bind <x> (accept))
    (make fact <x>))

;;;  Start
(start ((start)))

This program computes factorials in OPS-5. Some things seem to be
rather difficult to do in OPS-5. This same program could be 
written in several lines of lisp!