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From: cdsm@doc.ic.ac.uk (Chris Moss)
Newsgroups: comp.lang.prolog
Subject: Re: Thanks for the sour persimmons cousins, list syntax
Message-ID: <113@gould.doc.ic.ac.uk>
Date: Wed, 7-Oct-87 14:18:09 EDT
Article-I.D.: gould.113
Posted: Wed Oct  7 14:18:09 1987
Date-Received: Mon, 12-Oct-87 22:31:28 EDT
References: <5265@jade.BERKELEY.EDU> <2278@mulga.oz>
Reply-To: cdsm@gould.UUCP (Chris Moss)
Organization: Dept. of Computing, Imperial College, London, UK.
Lines: 27


In article <2278@mulga.oz> lee@mulga.UUCP (Lee Naish) writes:
>	H.T is more readable
>	H.T says the functor is '.' and there are two arguments, H and T
>	H.T is one less character
...
>[H|T] confuses people.  It has confused Prolog implementors!  There are
>Prolog implementations in which lists are not normal terms, due to this.
>Of course it is a shame that '.' and ',' are so overloaded in Prolog,
>but since '.' IS the list constructor functor, we may as well get it
>out in the open for all to see.

I have a lot of sympathy with this, and used to write all my conses with
a dot. But now I think it shouldn't be allowed. After all, nobody likes
writing full lists as a.b.c.d.[]. They always switch to [a,b,c,d] in the 
end. So it's more confusing having the two notations. Sure every IMPLEMENTOR
must know that '.' is the cons functor. But it helps to clean up error
handling if . on its own (i.e. not in a number or graphic symbol) is always 
the line terminator. Then one can get away from the silly errors like 
a(b).a(c). being treated as one clause.
Most of the other arguments (one less character etc.) are far less important
than the learning argument. Of course the best notation would be
[a b c . X] (have I seen that before?) but then . as a terminator would be
impossible.


Chris Moss..