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From: andrews@ubc-cs.UUCP (Jamie Andrews)
Newsgroups: net.lang.prolog
Subject: Re: "assert" considered harmful?
Message-ID: <269@ubc-cs.UUCP>
Date: Fri, 6-Jun-86 13:35:31 EDT
Article-I.D.: ubc-cs.269
Posted: Fri Jun  6 13:35:31 1986
Date-Received: Wed, 11-Jun-86 06:24:33 EDT
References: <1754@utai.UUCP>
Reply-To: andrews@ubc-cs.UUCP (Jamie Andrews)
Organization: UBC Department of Computer Science, Vancouver, B.C., Canada
Lines: 17


     I would say that if your only interest in Prolog is as a programming
language with neat features like backtracking and logic variables, then
by all means go ahead and use "assert" and "retract".  Just be aware of
how they affect the control flow in the program.

     It should be of little concern to applications programmers that
these features destroy the declarative reading of the program, unless they
have to prove to their bosses that their applications are rigourously
correct.  However, there are ways of implementing global variables and
assert-and-retract-like behaviour in a completely declarative setting;
see Shapiro's papers about concurrent Prolog and message-passing.  (The
object-oriented approach Shapiro advocates also explains I/O nicely.)

--Jamie.
...!seismo!ubc-vision!ubc-cs!andrews
"I believe in Santa Claus, and the DoD believes in Ada" -D.Parnas