Newsgroups: comp.lang.misc
Path: utzoo!utgpu!watserv1!tolstoy.waterloo.edu!mhcoffin
From: mhcoffin@tolstoy.waterloo.edu (Michael Coffin)
Subject: Programs as data
Message-ID: <1991Jun28.133708.3776@watserv1.waterloo.edu>
Keywords: lisp, prolog
Sender: news@watserv1.waterloo.edu
Organization: University of Waterloo
References: <4671@optima.cs.arizona.edu>
Date: Fri, 28 Jun 1991 13:37:08 GMT
Lines: 24

It's true that Prolog handles programs-as-data nicely, but I don't
think it's true that Prolog has a conventional syntax.  Other than
using infix notation, it looks nothing like any of the popular
languages.  That's not surprising; Prolog almost entirely lacks
explicit control structures, which are everywhere in conventional
languages. 

And unless you are willing to give up explicit control structures,
things are much more difficult than Prolog.  You have to devise ways
to represent not just infix notation, which has a fairly natural tree
representation, but while statements, case statements, for loops,
blocks, procedures, exit statements, ---the list goes on.  This has in
fact been done; I once saw a proposal for a Pascal-like language that
allowed programs as data.  Each control construct had an internal
format that amounted to a record with fields for each piece.  Most of
the fields, were, of course pointers to other records.  The result
was, in my opinion, a mess.

By the way, I think we ought to keep in mind that there are several
Lisps.  Common Lisp has a rather complicated syntax, as has been
pointed out.  Scheme, on the other hand, has a syntax that will fit on
a single page and leave room for comments.

-mike