Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-lcc!mordor!joyce!sri-unix!garth!smryan
From: smryan@garth.UUCP (Steven Ryan)
Newsgroups: comp.lang.misc
Subject: Re: Query re optimising hcrs
Message-ID: <1113@garth.UUCP>
Date: 30 Jul 88 21:13:37 GMT
References: <561@etive.ed.ac.uk> <24414@think.UUCP> <3678@hcr.UUCP>
Reply-To: smryan@garth.UUCP (Steven Ryan)
Organization: INTERGRAPH (APD) -- Palo Alto, CA
Lines: 13

>                     Only if the order that logical expressions is calculated
>is undefined is this optimization reasonable.

That is why it is better to leave the order of evaluation undefined.
 
>	if( (p != NULL) && (*p == VALUE) )
>
>where I check that the pointer is good and then check the value.  Reorganize
>this and all hell will break loose.

C, Algol60, and Algol68 provide an alternate construct which safe, explicit,
and lets the operators be just operators:

         if ( p==nil ? false : *p==value )