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From: ark@alice.UucP (Andrew Koenig)
Newsgroups: net.lang
Subject: Re: Operator Precedence
Message-ID: <4275@alice.UUCP>
Date: Thu, 5-Sep-85 18:26:03 EDT
Article-I.D.: alice.4275
Posted: Thu Sep  5 18:26:03 1985
Date-Received: Fri, 6-Sep-85 05:35:29 EDT
References: <262@pedsgd.UUCP>
Organization: Bell Labs, Murray Hill
Lines: 24

> I have a question. How did we end up with operator precedence in the
> first place? This seems to cause many more problems than what would
> seem to me to be obvious for algebraic expression - evaluate left
> to right in the absence of parenthesis. It seems to me that most
> programmers fully parenthesize anyway to avoid being bitten.
> Can anybody make a compelling case for not doing it this way?

OK, let's evaluate A=B+C strictly left to right.  First we copy B
into A, then we add C to A.  Now what do we do with the result?
Throw it away, I suppose.

I'm not being completely flip: that is exactly what C does if I
parenthesize the above expression so as to evaluate it strictly
left to right:    (A=B)+C

What to do?  Three solutions come to mind:

	1. Treat = specially.  This re-opens the precedence issue.

	2. Make assignment store into its RIGHT operand, as at
	   least one language (Neliac) has done.  Thus if we want
	   to set A to the sum of B and C, we write  B+C=A

	3. Make all operators group right to left, as APL has done.