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From: SHardy@SRI-KL@sri-unix.UUCP
Newsgroups: net.lang.prolog
Subject: Use of Assert
Message-ID: <12421@sri-arpa.UUCP>
Date: Mon, 10-Oct-83 23:39:07 EDT
Article-I.D.: sri-arpa.12421
Posted: Mon Oct 10 23:39:07 1983
Date-Received: Tue, 18-Oct-83 03:44:03 EDT
Lines: 27

A recent message on the use of Assert seemed to imply that it, and
Retract, shouldn;t be used because neither is well implemented on
the DEC-10 and both are, in fact, quite hard to implement.

In general, I think it a bad idea to object to using a feature of
a langauge because it is often badly impelemented.

If carried to an extreme, this view becomes silly.  I once saw an
article ``refuting'' the claim that Prolog was inefficient by
saying that the claimant had not programmed ``idiomatically''
(I.e. had used Assert) and so, presumably, deserved all he got.

Although Assert is ``not very logical'', it can be extremely useful.
Without Assert one could not implement SetOf.  Without SetOf all
kinds of things (such as making use of a closed world assumption)
are hard.

Crucially, Prolog now has several classes of user.  Some are
concerned with its purity and logical roots; others are concerned
with getting fast performance out of Prolog on Von Neumann machines;
others are concerned with using Prolog to solve some problem.

Why should the last group be bothered by the concerns of the first
two?

-- Steve Hardy,
   Teknowledge