Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!quintus!ok
From: ok@quintus.uucp (Richard A. O'Keefe)
Newsgroups: comp.lang.prolog
Subject: Re: Determining order of argument unification
Message-ID: <653@quintus.UUCP>
Date: 10 Nov 88 01:35:30 GMT
References: <8192@burdvax.PRC.Unisys.COM> <1028@murtoa.cs.mu.oz.au> <8249@burdvax.PRC.Unisys.COM>
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Reply-To: ok@quintus.UUCP (Richard A. O'Keefe)
Organization: Quintus Computer Systems, Inc.
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In article <8249@burdvax.PRC.Unisys.COM> lang@zeta.PRC.Unisys.COM (Francois-Michel Lang) writes:
>As the instigator of what I had intended as nothing more than
>a fairly simple and informal puzzle, I apologize for having
>roused the infamous O'Keefe dragon and prompted him to unleash
>yet another onslaught of his matchless prose.

Checking a dictionary, I find
    infamous a. 1. notorious 2. shocking
    notorious a. 1. known for something bad ...

>I stand corrected in my claim that LR and RL argument evaluation
>are the only two "reasonable" orders.  Lee and Richard,
>would you perhaps grant that LR and RL are "the two most
>obvious or most commonly used" orders, which is perhaps
>what I should have said to begin with?

The most obvious, certainly.  The most commonly used?  I have no idea.
What I can be reasonably confident about is that few if any WAM-based
compilers will use either order.  "Usually LR" is what you'll get.
I don't know about PopLog, but it *used* to use predominantly RL,
but it would break off chunks of the head and hand them to a general
unification routine if the head was too complex.  Early versions of
Prolog-X were strictly LR, mainly to make decompilation easier.

>Thanks to Lee for posting a response to my original question
>which correctly answers it in the *spirit* in which it was asked!

As I pointed out, if one has read the relevant paper (and I have),
the intended answer was obvious, so I _couldn't_ solve the puzzle.
All I could do was point out that the obvious answer is wrong.
I'm sorry if that seems like an onslaught (=attack).