Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!brutus.cs.uiuc.edu!apple!fox!portal!cup.portal.com!pgl
From: pgl@cup.portal.com (Peter G Ludemann)
Newsgroups: comp.lang.prolog
Subject: Re: Prefix operators and blanks (was: WG17)
Message-ID: <24783@cup.portal.com>
Date: 7 Dec 89 07:00:13 GMT
References: <24703@cup.portal.com> <2892@munnari.oz.au>
Organization: The Portal System (TM)
Lines: 29

The only canonical way of writing out a compound term so that
it can be read in without regard to operator definitions is to
quote everything and use no operator notation.  For example:

	a+b		===>	'+'('a','b')
	:- (a,b)	===>	':'(','('a','b'))

Why all the quotes?  Well, someone could have defined `a' to be
an operator and therefore '+'(a,b) would get a syntax error.

What I am suggesting is that if `+' is an operator, then you will
be forbidden to write in your program:

	+(a,b)		or
	+ (a,b)

You must write instead:

	'+'(a,b)	or
	'+'((a,b))	etc.

(BTW, there is no ambiguity if comma is not an operator.  That is
the one big advantage of the Waterloo syntax - `&' is used instead
and comma is only used as an argument separator.  But I am NOT
suggesting deviating that far from Edinburgh syntax.)

- peter ludemann	pgl@cup.portal.com   sun!portal!cup!pgl

	--- standard disclaimer ---