Path: utzoo!attcan!uunet!munnari.oz.au!goanna!ok
From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.lang.lisp
Subject: Re: Virtues(?) of Lisp syntax
Keywords: syntax words, functions, redundancy, cognitive engineering
Message-ID: <3785@goanna.cs.rmit.oz.au>
Date: 18 Sep 90 12:43:53 GMT
References: <3368@skye.ed.ac.uk> <1350030@otter.hpl.hp.com> <3408@skye.ed.ac.uk> <3465@syma.sussex.ac.uk>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 52

In article <3465@syma.sussex.ac.uk>, aarons@syma.sussex.ac.uk (Aaron Sloman) writes:
> Prolog has yet another kind of syntactic poverty, inherited from its
> dependence on a logical interpretation. (E.g. textual order has very
> different procedural meanings depending on context: within a rule
> concatenation means something like "and then", whereas between rules
> with the same predicate it means something like "and if that fails
> then try...")

Not to defend Prolog syntax overmuch, but I had to stop and think for
several minutes before I understood what Aaron Sloman was getting at
here.  It had never occurred to me that

	p :-		%  p <if>		
		a,	%	a <and-then>
		b.	%	b.

and
	p(a).		% either p(a)
	p(b).		% or-else p(b)

were both "concatenation".  For sequencing of clauses, yes it is plain
juxtaposition.  But and-then is an explicit operator ",", not mere
concatenation.  I have always experienced these two constructions as
utterly different, and it is very hard for me to see them as similar.
If we wrote
	(((p)		; p if
		(a)	;	a and-then
		(b)))	;	b
and
	(((p a))	; either p(a)
	 ((p b)))	; or-else p(b)
_then_ we would be using juxtaposition of lists for both.

> For the record, I should also say that I don't think there's much
> difference in readability between the following:
 
>     a(b(c(d, e), f(g, h)))      [Pop-11 and Pascal, etc]
 
>     (a (b (c d e) (f g h)))     [Lisp]

I was about to agree, and then I suddenly realised that I find the
second distinctly easier to read.  Hang on a minute, I'm a _Prolog_
programmer, what's going on here?

Just for fun, here's a Pop-2 statement that does the same function calls:

	d, e.c, g, h.f.b.a;

Not to knock Pop.  If Scheme is the Messiah, Pop is John the Baptist.
[It's a _joke_, Joyce.]
-- 
Heuer's Law:  Any feature is a bug unless it can be turned off.