Transformations of CCP programs

Abstract

We introduce a transformation system for concurrent constraint programming (CCP). We define suitable applicability conditions for the transformations which guarantee that the input/output CCP semantics is preserved also when distinguishing deadlocked computations from successful ones and when considering intermediate results of (possibly) non-terminating computations.The system allows us to optimize CCP programs while preserving their intended meaning: In addition to the usual benefits that one has for sequential declarative languages, the transformation of concurrent programs can also lead to the elimination of communication channels and of synchronization points, to the transformation of non-deterministic computations into deterministic ones, and to the crucial saving of computational space. Furthermore, since the transformation system preserves the deadlock behavior of programs, it can be used for proving deadlock freeness of a given program with respect to a class of queries. To this aim it is sometimes sufficient to apply our transformations and to specialize the resulting program with respect to the given queries in such a way that the obtained program is trivially deadlock free.

Unfolding for CHR programs

“…This step could be extended in several directions: First of all, the unfolding operation could be extended to take into account also the constraints in the propagation part of the head of a rule. Also, we could extend to CHR some of the other transformations, notably folding (Tamaki and Sato 1984) which has already been applied to CCP in (Etalle et al 2001). Finally, we would like to investigate from a practical perspective to what extent program transformation can improve the performance of the CHR solver.…”

Specialization of Concurrent Guarded Multi-set Transformation Rules

“…Since CHR can be seen as an extension of concurrent constraint programming (CCP) [SR90] by multiple heads (multi-sets) and propagation rules, literature on program transformation for concurrent constraint and logicbased programming languages is relevant: [EGM01] deals with transformations of concurrent constraint logic programs, [FPP04] deals with constraint logic programs (CLP), and [UF88] deals with a guarded concurrent logic programming language called GHC.…”

“…-In concurrent languages like CHR, we also can eliminate communication channels, synchronization points and don't care nondeterminism [EGM01]. -Verification and model checking can be done by program transformation [DP99,FPP01,RKRR04].…”

“…-Verification and model checking can be done by program transformation [DP99,FPP01,RKRR04]. -Agent can be specialized to a specific context (Example in [EGM01]). …”

Termination of simply moded logic programs with dynamic scheduling

“…Indeed, standard semantics for concurrent logic languages such as CCP [13,25] and GHC [31] often capture such intermediate results, or in any case, the results of non-successful computations [11]. In fact, input consuming programs can have a reactive nature: the (partial) result of a computation may trigger another computation by instantiating sufficiently the input positions of another atom so that it becomes resolvable.…”