Restricting Variable Domain without CLPFD Library

Question

I have a list of variables in my program, say A, B, C, D, ..., J, and I need to restrict the domain of each of the variables to the same set of integers, say 1, 2, ... 10. I know of a few different ways to do this, but all of them use at least one method from CLPFD, such as X #> 0, X ins [domain], or fd_domain(args). I haven't been able to find a way of doing this without any built-in libraries (all of which are banned for this project).

I would think that writing in the rules like this would be sufficient:

A > 0, A < 11, B > 0, B < 11, ..., J > 0, J < 11

But apparently the variables are not sufficiently instantiated. I know it's a trivially simple question, but I've been searching on my own for a while and really have no other resources for help. Thanks very much.

Fred Foo Fred Foo · Accepted Answer · 2013-11-17T17:31:32

There's the between function in SWI-Prolog:

?- between(1, 9, A).
A = 1 ;
A = 2 ;
A = 3 ;
A = 4 ;
A = 5 ;
A = 6 ;
A = 7 ;
A = 8 ;
A = 9.

If that's banned as well (it's non-standard), then you use member/2:

?- member(A, [1, 2, 3, 4, 5, 6, 7, 8, 9]).
A = 1 ;
A = 2 ;
A = 3 ;
A = 4 ;
A = 5 ;
A = 6 ;
A = 7 ;
A = 8 ;
A = 9.

Without CLP(fd), you'll be trapped in the generate-and-test paradigm, though, and perhaps it's better to find some workaround where you check variable values in an ad hoc way to get decent performance.

Restricting Variable Domain without CLPFD Library

1 Answers