Constraint logic programming: Difference between revisions

Revision as of 17:23, 8 March 2006

Revision as of 17:44, 8 March 2006

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===Reals===

Constraint logic programming with [[real numbersnumber]]s uses real expressions as terms. When no functors are used, terms are expressions over reals, possibly including variables. In this case, each variable can only take a real number as a value.

Precisely, terms are expressions over variables and real constants. Equality between terms is a kind of constraint that is always present, as the interpreter generates equality of terms during execution. As an example, if the first literal of the current goal is <code>A(X+1)</math> and the interpreter has chosen a clause that is <code>A(Y-1):-Y=1</code> after rewriting is variables, the constraints added to the current goal are <code>X+1=Y-1</code> and <math>Y=1</math>. The rules of simplification used for functors are obviously not used: <code>X+1=Y-1</code> is not unsatisfiable just because the first expression is built using <code>+</code> and the second using <code>-</code>.

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Equality of two terms can be simplified using the rules for tree terms if none of the two terms is a real expression. For example, if the two terms have the same functor and number of subterms, their equality constraint can be replaced with the equality of subterms.

===Finite domains===

The third class of constraints used in constraint logic programming is that of finite domains. Values of variables are in this case taken from a finite ___domain, which is usually identified with that of [[integer number]]s.

==Reference==