Path: utzoo!mnetor!uunet!husc6!sri-unix!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.lang.prolog
Subject: Re: behavior of read/get0 at end_of_file
Message-ID: <787@cresswell.quintus.UUCP>
Date: 19 Mar 88 03:04:08 GMT
References: 608 <1197@kulcs.kulcs.uucp> <783@cresswell.quintus.UUCP>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 24
Keywords: get0 read end_of_file BSI

In article <783@cresswell.quintus.UUCP>, I replied to article
<1197@kulcs.kulcs.uucp>, by bimandre@kulcs.uucp (Andre Marien)
[signed by Andre Marien and Bart Demoen both].
The topic was what read/1 and get0/1 should do at the end of a stream.

I thought you might be interested to know what the BSI committee say.

In document PS/236, "Draft minutes, Prolog Built-In Predicates meeting,
10 December 1987", we find

	4 Design criterion

	<name deleted> suggested: "Whenever possible, a predicate with
	a side effect should always succeed and never instantiate
	variables."

This of course rules get0/1 and read/1 out entirely.  That may not be
what <name deleted> _meant_, but it _is_ what the minutes say he _said_.
As far as I can tell, the real intent is to rule out retract/1, which
is disliked because it unifies its argument with the thing you removed.
The minutes show that Paul Chung proposed naming the standard clause-
removing predicate delete/1 instead of retract/1.  Good on yer, mate!
This should not be construed as endorsement of the name delete/1, but
as praise for Paul Chung's good standardisation manners.