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From: g-rh@cca.UUCP (Richard Harter)
Newsgroups: net.lang
Subject: Re: and if you put this in your language ...
Message-ID: <6699@cca.UUCP>
Date: Sat, 15-Mar-86 18:19:26 EST
Article-I.D.: cca.6699
Posted: Sat Mar 15 18:19:26 1986
Date-Received: Mon, 17-Mar-86 03:27:19 EST
References: <1187@mmintl.UUCP> <>
Reply-To: g-rh@cca.UUCP (Richard Harter)
Organization: Computer Corp. of America, Cambridge
Lines: 55
Summary: 

In article <> taylor@glasgow.UUCP (Jem Taylor) writes:
>	..................
>	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.
>
	Sorry Jem, the code you suggest is wrong in principle
even though it may be the right thing to do in practice as a
matter of convenience, the principle bei:

	AVOID USING MULTIPLE COPIES OF THE SAME CODE

Procedures are one way to avoid multiple copies.  In any particular
instance, however, creating another procedure may well be the wrong
thing to do.  The most general solution is to use a flag (which, as
I recall, people were objecting to originally), e.g.

	flag = 0;
	if (A) {
	   X;
	   if (B) Y;
	   else flag = 1;
	   }
	else flag = 1;
	if (flag) Z;

[I'm not in love with this code either.]  If X, Y, and Z are large
blocks of code one might also consider:

	xflag = 0;
	yflag = 0;
	zflag = 0;
	if (A) xflag = 1;
	else   zflag = 1;
        if (xflag) {
	   X;
	   if (B) yflag = 1;
	   else   zflag = 1;
	   }
	if (yflag) Y;
	if (zflag) Z;

This is more long winded in schematic form.  However it will be clearer
if X, Y, and Z are complicated pieces of code.

[All complaints about the above style of indentation will be forwarded
to /dev/null or to Rich Rosen.]

	Richard Harter, SMDS Inc.