Simple question - XSB Prolog

Question

Hello!

I'm diving into the world of prolog headfirst but I seem to have hit shallow water!

I'm looking at database manipulation in prolog with regards to this tutorial:Learn Prolog Now!

It states that I can see my database by entering listing

So i tried it and it should basically output everything in my .P file(facts, rules), but this is what i get, here are my sequence of commands:

? consult('D:\Prolog\testfile.P').
[testfile.P loaded]

? listing.

library_directory(C:blahblahpathtoXSB)
library_directory(C:blahblahXSBpath)
{this is listed around 5 times)}

shouldn't this command display what is in testfile.P, according to the tutorial? also, after consult testfile.P i should be ableto use assert to add more facts but it doesnt actually change anything in the testfile.P..?

any ideas

Answer 1

The behavior of the listing predicate varies by Prolog interpreter. The XSB documentation explains what code will be included in the output of listing/0:

Note that listing/0 does not list any compiled predicates unless they have the dynamic property (see predicate property/2). A predicate gets the dynamic property when it is explicitly declared as dynamic, or automatically acquires it when some clauses for that predicate are asserted in the database.

With a very simple test.P file containing this:

test(a,b).

Here is using listing/0 in XSB with both the consulted file and an asserted rule. It only outputs the dynamically asserted rule, not the contents of the file:

| ?- consult('test.P').
[test loaded]

yes
| ?- listing.
library_directory(/home/jeffd/xsb/XSB/packages).
library_directory(/home/jeffd/xsb/XSB/site/lib).
library_directory(/home/jeffd/xsb/XSB/site/config/i686-pc-linux-gnu/lib).
library_directory(/home/jeffd/xsb/XSB/config/i686-pc-linux-gnu/lib).
library_directory(/home/jeffd/.xsb/config/i686-pc-linux-gnu).

yes
| ?- assert(testing(c,d)).

yes
| ?- listing.
testing(c,d).

library_directory(/home/jeffd/xsb/XSB/packages).
library_directory(/home/jeffd/xsb/XSB/site/lib).
library_directory(/home/jeffd/xsb/XSB/site/config/i686-pc-linux-gnu/lib).
library_directory(/home/jeffd/xsb/XSB/config/i686-pc-linux-gnu/lib).
library_directory(/home/jeffd/.xsb/config/i686-pc-linux-gnu).

SWI-Prolog behaves the way Learn Prolog Now describes and outputs the contents of both files and dynamically added rules:

?- consult('test.P').
% test.P compiled 0.00 sec, 1,192 bytes
true.

?- assert(testing(c,d)).
true.

?- listing.

test(a, b).

%   Foreign: rl_read_history/1

:- dynamic testing/2.

testing(c, d).

%   Foreign: rl_write_history/1

%   Foreign: rl_add_history/1

%   Foreign: rl_read_init_file/1
true.