Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!pyrnj!pyrdc!uunet!mcvax!ukc!dcl-cs!simon
From: simon@comp.lancs.ac.uk (Simon Brooke)
Newsgroups: comp.lang.prolog
Subject: Re: The meaning of "declarative"
Message-ID: <590@dcl-csvax.comp.lancs.ac.uk>
Date: 17 Oct 88 15:11:51 GMT
References: <ALF.88Oct2184429@hathor.sics.se> <818@etive.ed.ac.uk>
Reply-To: simon@comp.lancs.ac.uk (Simon Brooke)
Distribution: comp.lang.prolog
Organization: Department of Computing at Lancaster University, UK.
Lines: 55

In article <818@etive.ed.ac.uk> jha@lfcs.ed.ac.uk (Jamie Andrews) makes some
assertions which I find contentious:
>
>     BTW, re. my comment about functional programming:  logic
>programming uses the language of logic, which is (by definition,
>almost) very close to the way we think and deduce information
>from assumptions.  

Oh, come on now! Very, very few people can even be taught logic. Most of
those who can will always find it excrutiatingly difficult. It is a most
unnatural and tedious way of 'deducing information from assumptions'; and
if you cand find anyone who thinks logically, I wish you'ld introduce them
to me - it would be a new and fascinating experience.

>So logic programming is very useful for
>systems with lots of logical dependencies (expert systems,

That's a pretty bald assertion, too. The resolution theorem prover is not
good either at handling uncertainty or at generating highlevel explanation
traces; consequently, to implement an expert system, you essentially have
to implement a new inference mechanism. But my experience (and judging by
the lack of Prolog-based expert systems out there in the real world, other
people's, too) is that Prolog is not an easy language in which to write an
inference engine.

>protocol testers, etc.), and its structure corresponds to a wide
>class of problems.  Functional programming can make no such
>claim -- very few problems seem better thought of in terms of
>mathematical functions.  The main thing that functional
>programming seems to offer over relational is a clear and
>deterministic decision procedure.
>
Well yes, and that's a serious point. The notion that you can write 
declarative code in Prolog is a nice one, and it may be that there are
some people out there who can do it. Me, I can't, and God knows I've tried.
Furthermore, I haven't seen any significant chunk of declarative code written
in Prolog by anyone else either. Most Prolog programs which do anything useful
are procedural; but when a piece of procedural Prolog goes wrong, it is 
(in my experience) horrible to debug.

>--Jamie.
>  jha@lfcs.ed.ac.uk
>"I always find mathematics so difficult" -- D.Hilbert

And as for David #@%*&!* Hilbert and his assertion that '...after w (omega),
counting continues naturally w+1, w+2, w+3...' I don't believe it and
never did.


** Simon Brooke *********************************************************
*  e-mail : simon@uk.ac.lancs.comp                                      * 
*  surface: Dept of Computing, University of Lancaster,  LA 1 4 YW, UK. *
*                                                                       *
*  Thought for today: isn't it time you learned the Language            * 
********************* International Superieur de Programmation? *********