Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!tymix!cirrusl!ss168!dhesi
From: dhesi%cirrusl@oliveb.ATC.olivetti.com (Rahul Dhesi)
Newsgroups: comp.lang.c
Subject: Re: Terminology
Keywords: expression definition
Message-ID: <3055@cirrusl.UUCP>
Date: 15 Apr 91 22:05:44 GMT
References: <1917@manta.NOSC.MIL>
Sender: news@cirrusl.UUCP
Organization: Cirrus Logic Inc.
Lines: 30

In <1917@manta.NOSC.MIL> mitch@manta.NOSC.MIL (Ray Mitchell) tries
to define an "expression":

    "Any combination of constants, variables, and operators (producing
     a value)"

     It seems intuitively clear that an expression must have a
     value...  However, how about a function returning "void" or an
     expression cast to type "void"?

In colloquial technical English, an expression is any entity that has a
value.  Therefore a function returning "void" is not an expression.
The purpose of introducing such functions into C was to belatedly add
procedures to the language.  Languages that have procedures don't need
void-returning functions.

But when you define a programming language, the concept of "expression"
as described above is not necessary.  Languages that use the term
"expression" use it only as a syntactic token to which some meaning
must be separately assigned.  Instead of saying "expression" you can
say "gadget" or "whatist" without losing any information.  So, if the
grammar of a language (e.g. C) allows an "expression" to be, among
other things, a function returning void, it's purely for notational
convenience.

In other words, "expression" means whatever you want it to mean.  A
function returning void is not an expression--unless you say so.
--
Rahul Dhesi <dhesi@cirrus.COM>
UUCP:  oliveb!cirrusl!dhesi