Simple Constraint Logic Programming sample CLP(Q) gives error in Prolog

Question

I've started to learn Prolog and I follow the RIPTutorial PDF. At the Constraint Logic Programming CLP(Q) section, it says:

Constraint Logic Programming CLP(Q) implements reasoning over rational numbers

Example:

?- { 5/6 = X/2 + 1/3 }.
X = 1.

When I've tried this line on SWI-Prolog on Windows, it gave:

ERROR: Unknown procedure: {}/1 (DWIM could not correct goal)

The same line on commandline SWI-Prolog-7.2.0 on macOS gives:

ERROR: toplevel: Undefined procedure: {}/1 (DWIM could not correct goal)

How to get the expected output of X = 1. ?

@jkiiski No, I didn't. In the tutorial, there was no mention of any library. — Lars Malmsteen, Jul 24 '21 at 10:41
@Guy Coder, when I entered `use_module(library(clpr)).` it worked out okay. In the tutorial there was no mention of `use_module` — Lars Malmsteen, Jul 24 '21 at 10:44
@GuyCoder: The question applies to many Prologs alike. In fact, SICStus was first in the early 1990s to feature that very `clpq` library. Reserve the swi-prolog tag to questions that are specific to SWI alone. — false, Jul 25 '21 at 16:06

score 3 · Accepted Answer · answered Jul 25 '21 at 09:55

3

As noted in the comments you need to load the code for CLP(Q) first.

?- use_module(library(clpq)).
true

Then enter the query as in the example.

?- {5/6 = X/2 + 1/3}.
X = 1.

answered Jul 25 '21 at 09:55

Guy Coder

1 Answers1