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From: weikart@prl.dec.com (Chris Weikart)
Newsgroups: comp.lang.c++
Subject: Re: simplifying C++
Message-ID: <1991Mar5.195042.6263@prl.dec.com>
Date: 5 Mar 91 19:50:42 GMT
References: <5.UUL1.3#8618@softrue.UUCP>
Sender: news@prl.dec.com (USENET News System)
Reply-To: weikart@prl.dec.com (Chris Weikart)
Organization: Digital Equipment Corporation - Paris Research Laboratory
Lines: 51

In article <5.UUL1.3#8618@softrue.UUCP>, kearns@softrue.UUCP (Steven
Kearns) writes:
|> 
|> Here is another in the continuing series:  "Simplifying C++".  
|> 
|> Expression languages are languages where each statement returns a
|> value.
|> Lets make C++ an expression language as follows:
|> 
|> 	Expression Statements, like "a = 5;", return the value of the 
|> 		expression.
|> 	"if (e1) s1; else s2;" returns the value of s1 if e1 true,
|> otherwise
|> 		it returns the value of s2.  If s1 and s2 
|> 		return values of different types, the "if" returns a void.
|> 	"{s1; s2; s3;} returns the value of the last statement in the
|> 		compound statement. 
|> 	All other statements, including an if statement without an else,
|> 		return void.
|> 
|> The advantage of this is manyfold: first, we get to eliminate the
|> comma operator, which is used to evaluate multiple expressions as in
|> (e1, e2, e3).  Instead, you can write {e1; e2; e3;}.  Also, we can
|> eliminate the ugly (B ? e1 : e2) syntax, writing (if (B) e1; else
|> e2;) 
|> instead.
|> 
|> Also, you can do things impossible before, for example declaring
|> variables inside expressions:
|> 
|> 	if {int i = f(a, b); i >=3 && i <= 33;}
|> 		cout << "hi there";
|> 
|> We probably want to disallow "gotos" and "returns" inside a compound
|> statement used as an expression.  
|> 
|> -steve
|> 
|> ********************************************************
|> * Steven Kearns            ....uunet!softrue!kearns    *
|> * Software Truth           softrue!kearns@uunet.uu.net *
|> ********************************************************

The comma operator must have been invented for "for" loops; it's
usefulness in macros was, in my opinion, unforeseen and fortuitous.
"For" loops require a separator with lower (or higher? I can never get
this straight) priority than the ";" in order to allow multiple
expressions for each of the three parts.

-------------------------------------------------------------------------------
Chris Weikart <weikart@dec.prl.com> .............. DEC Paris Research Lab (PRL)