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From: neubauer@bsu-cs.UUCP (Paul Neubauer)
Newsgroups: comp.lang.pascal
Subject: Re: Pascal User Manual and Report
Message-ID: <2149@bsu-cs.UUCP>
Date: 18 Feb 88 14:56:46 GMT
References: <169900010@uiucdcsb>
Organization: CS Dept, Ball St U, Muncie, Indiana
Lines: 28

In article <169900010@uiucdcsb>, wsmith@uiucdcsb.cs.uiuc.edu writes:
> I was just looking at Jensen & Wirth's _Pascal User Manual and Report_.  
> In the section on the AND and OR operators, it says:
> "Assume for example, that x=0.  Then 
> 	(x>0) and (x<10)
> is already known to be false after computation of the first factor, and the
> scond need not be evaluated.  The rules of Pascal neither require nor forbid
> 						  ^^^^^^^^^^^^^^^
> the evaluation of the second part in such cases."
> 
> Is this still true in the "current definition" of Pascal.  All of the
> implementations I've found will evaluate the second part.  

It turns out that this is not quite true.  VAX Pascal does not (necessarily)
evaluate the second part.  I am not completely sure if this behavior depends
on optimization levels or some such, but around here, the local default is
/NOOPTIMIZE and even something like:

	x := 1;
	y := 0;
	IF (x < y) AND (x/y <> 1) THEN
		...

will not crash.

-- 
Paul Neubauer         neubauer@bsu-cs.UUCP
                      <backbones>!{iuvax,pur-ee,uunet}!bsu-cs!neubauer