Constraint logic programming: Difference between revisions

Revision as of 14:53, 26 February 2010

Revision as of 11:47, 22 April 2010

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Actual interpreters process the goal elements in a [[LIFO (computing)|LIFO]] order: elements are added in the front and processed from the front. They also choose the clause of the second rule according to the order in which they are written, and rewrite the constraint store when it is modified.

The third possible kind of transition is a replacemenetreplacement of the constraint store with an equivalent one. This replacement is limited to those done by specific methods, such as [[constraint propagation]]. The semantics of constraint logic programming is parametric not only to the kind of constraints used but also to the method for rewriting the constraint store. The specific methods used in practice replace the constraint store with one that is simpler to solve. If the constraint store is unsatisfiable, this simplification may detect this unsatisfiability sometimes, but not always.

The result of evaluating a goal against a constraint logic program is defined if the goal is proved. In this case, there exists a derivation from the initial pair to a pair where the goal is empty. The constraint store of this second pair is considered the result of the evaluation. This is because the constraint store contains all constraints assumed satisfiable to prove the goal. In other words, the goal is proved for all variable evaluations that satisfy these constraints.