Concurrent constraint logic programming: Difference between revisions

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Syntactically, concurrent constraints logic programs are similar to non-concurrent programs, the only exception being that clauses include [[Guard (computing)|guards]], which are constraints that may block the applicability of the clause under some conditions. Semantically, concurrent constraint logic programming differs from its non-concurrent versions because a goal evaluation is intended to realize a concurrent process rather than finding a solution to a problem. Most notably, this difference affects how the interpreter behaves when more than one clause is applicable: non-concurrent constraint logic programming [[Recursion|recursively]] tries all clauses; concurrent constraint logic programming chooses only one. This is the most evident effect of an intended ''directionality'' of the interpreter, which never revise a choice it has previously taken. Other effects of this are the semantical possibility of having a goal that cannot be proved while the whole evaluation does not fail, and a particular way for equating a goal and a clause head.

[[Constraint handling rules]] can be seen as a form of concurrent constraint logic programming,<ref>Frühwirth, Thom. "[https://www.sciencedirect.com/science/article/pii/S0743106698100055 Theory and practice of constraint handling rules]." The Journal of Logic Programming 37.1-3 (1998): 95-138.</ref> but are used for programming a constraint simplifier or solver rather than concurrent processes.

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