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Re: Bug with streams or listing?

From: Lindsey Spratt
Subject: Re: Bug with streams or listing?
Date: Sun, 6 Nov 2005 11:58:34 -0500

The problem here is that listing/1 does not write to stdout (which is what tell/1 redirects) but rather to top_level_output. I don't know if there's any way to redirect top_level_output. (I would think listing/1 *should* use stdout.)

You can write listing/1 to an arbitrary stream using a *mirror*:

?- open('foo', write, S), add_stream_mirror(top_level_output, S), listing(kb), close(S).

This will write the listing for kb to file 'foo'.

Lindsey Spratt

On Nov 6, 2005, at 10:46 AM, Daniel Savard wrote:

Seems there is a bug with the streams implementation. I am newbie to
both gnu-prolog and prolog, I am trying to save a knowledge base using
the following fragment of code. This code is working properly with
swi-prolog-lite, but not with gnu-prolog. Only the write statement
produce some output in the file, the listing predicate is generating
output to the screen as if the user_output stream has not been
redirected into the file bozo.pl. A write after listing will output to
the file as expected. What is going wrong with listing? Is there a
work around?


Assume the output file is bozo.pl and the knowledge base is kb and in
file toto.pl.

I tried as well this way with the same result, working fine with

tell('bozo.pl'),write(':- dynamic(kb/2).'),nl,listing(kb),told.

I am running gnu-prolog 1.2.16 with Linux kernel 2.6.13.


Daniel Savard

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