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From: ark@rabbit.UUCP
Newsgroups: net.lang.c
Subject: Re: Must useless expressions be evaluated?
Message-ID: <2076@rabbit.UUCP>
Date: Sun, 16-Oct-83 12:33:09 EDT
Article-I.D.: rabbit.2076
Posted: Sun Oct 16 12:33:09 1983
Date-Received: Mon, 17-Oct-83 01:56:03 EDT
References: <817@mit-eddie.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 11

Barry Margolin points out that if foo is a reducible function,
then the compiler is allowed to generate code for

	if bool_var | foo(x) then ...

which does not evaluate foo if bool_var is true.  This statement
is correct, but slightly misleading -- the PL/I implementation
I have used (and, if I recall correctly, the ANSI standard) permits
the compiler to use short-circuit evaluation in this context even
if foo is not reducible.  In general, the compiler is only obliged
to evaluate enough of an expression to determine its result.