Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!think.com!snorkelwacker.mit.edu!ai-lab!rice-chex!bson
From: bson@rice-chex.ai.mit.edu (Jan Brittenson)
Newsgroups: comp.sys.handhelds
Subject: Re: DEC2FRAC-II for the HP48SX
Message-ID: <14393@life.ai.mit.edu>
Date: 27 Mar 91 20:51:18 GMT
References: <27efcf56:1772.1comp.sys.handhelds;1@hpcvbbs.UUCP> <40605@cup.portal.com> <1991Mar27.125528.7914@en.ecn.purdue.edu>
Sender: news@ai.mit.edu
Organization: nil
Lines: 37

In a posting of [27 Mar 91 12:55:28 GMT]
   wscott@en.ecn.purdue.edu (Wayne H Scott) writes:

 > 2: '.5*X-.75'
 > 1: 10
 > DEC2FRAC			<-- ->Q works this way but I don't know how
 > 1: '1/2*X-3/4'			   to duplicate it.


   The following program used ->Q instead of DEC2FRAC (only for
illustrative purposes, I don't have DEC2FRAC at hand):

DO->Q:

<< IFERR OBJ-> 			@ Break up algebraic
   -> n oper			@ Save operand count and operator (e.g. +)
     << 1 n START		@ Loop operands
	  DO->Q			@ Convert operand
	  n ROLL		@ Move to next operand circularly
	NEXT
	oper EVAL		@ Join back together
     >>
   THEN ->Q END			@ Not algebraic - apply your ->Q here
>>


Thus, '(.5+.2)/.1' DO->Q results in '(1/2+1/5)/(1/10)'

   Limitations are of course arguments made up of lists, programs,
strings, etc, that are acceptable to OBJ->. The IFERR construct can be
replaced by a rather extensive type check, much easier done with
system RPL. I didn't keep Joe's DEC2FRAC (assuming I can get it from
your server whenever I need it), but the code above should be fairly
trivial to adapt to it. (So we'll leave that as a reader exercise.)

						-- Jan Brittenson
						   bson@ai.mit.edu