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From: taylor@glasgow.glasgow.UUCP (Jem Taylor)
Newsgroups: net.lang
Subject: Re: and if you put this in your language ...
Message-ID: <447@glasgow.glasgow.UUCP>
Date: Wed, 12-Mar-86 16:37:53 EST
Article-I.D.: glasgow.447
Posted: Wed Mar 12 16:37:53 1986
Date-Received: Sat, 15-Mar-86 21:35:13 EST
References: <1187@mmintl.UUCP>
Reply-To: taylor@glasgow.UUCP (Jem Taylor)
Organization: Comp Sci Dept, Glasgow Univ, Scotland
Lines: 28

In article <1187@mmintl.UUCP> franka@mmintl.UUCP (Frank Adams) writes:
>One often winds up writing this in the form:
>   if (A) then X;
>   if (A && B) then Y; else Z;
>However, this fails if executing X changes the value of A (or if A has side
>effects); and if evaluating A is expensive, the additional evaluation may be
>undesirable.  In languages where the order of execution is not specified for
>the 'and' operator, the evaluation of (A && B) may fail if evaluation of B
>is not valid unless A is true and/or X has been executed (which is fairly
>common).
>
>In C, one often sees something like:
>
>   if (A &&  (X, B)) then Y; else Z;
>
>However, this only works if X can be written in-line.
>
	if (A)
	{	X;
		if (B)	Y;
		else	Z;
	}
	else	Z;

If Z is so large that it is not reasonable to have two copies of it's code, it's
time to make it a separate procedure anyway.

-Jem.