A hyperdoctrinal view of concurrent constraint programming

BRICS Report Series, 2002

The tcc paradigm is a formalism for timed concurrent constraint programming. Several tcc languages differing in their way of expressing infinite behaviour have been proposed in the literature. In this paper we study the expressive power of some of these languages. In particular, we show that:<dl compact="compact"><dt>(1)</dt><dd>recursive procedures with parameters can be encoded into parameterless recursive procedures with dynamic scoping, and vice-versa.</dd><dt>(2)</dt><dd>replication can be encoded into parameterless recursive procedures with static scoping, and vice-versa.</dd><dt>(3)</dt><dd>the languages from (1) are strictly more expressive than the languages from (2).</dd></dl>Furthermore, we show that behavioural equivalence is undecidable for the languages from (1), but decidable for the languages from (2). The undecidability result holds even if the process variables take values...

Theoretical Computer Science, 1993

[1993] Proceedings Eighth Annual IEEE Symposium on Logic in Computer Science

We propose a framework for the analysis of concurrent constraint programming (ccp). Our approach is based on simple denotational semantics which approximate the usual semantics in the sense that they give a superset of the input-output relation of a ccp program. Analyses based on these semantics can be easily and efficiently implemented using standard techniques from the analysis of logic programs. 1 Introduction Concurrent constraint programming (ccp) [12, 13, 14] is a new programming paradigm which elegantly combines logical concepts and concurrency mechanisms. The computational model of ccp is based on the notion of constraint system, which consists of a set of constraints and an entailment (implication) relation. Processes interact through a common store. Communication is achieved by telling (adding) a given constraint to the store, and by *This work has been partially supported by ESPRIT BRA

Theoretical Computer Science, 1997

Concurrent constraint programming (ccp), like most of the concurrent paradigms, has a mechanism of global choice which makes computations dependent on the scheduling of processes. This is one of the main reasons why the formal semantics of ccp is more complicated than the one of its deterministic and local-choice sublanguages. In this paper we study various subsets of ccp obtained by adding some restriction on the notion of choice, or by requiring con uency, i.e. independency from the scheduling strategy. We show that it is possible to de ne simple denotational semantics for these subsets, for various notions of observables. Finally, as an application of our results we develop a framework for the compositional analysis of full ccp. The basic idea is to approximate an arbitrary ccp program by a program in the restricted language, and then analyze the latter, by applying the standard techniques of abstract interpretation to its denotational semantics.

The Journal of Logic Programming, 1997

The standard operational semantics of concurrent constraint logic languages is not confluent in the sense that different schedulings of processes may result in different program behaviors. While implementations are free to choose specific scheduling policies, analyses should be correct for all implementations. Moreover, in the presence of parallelism, it is usually not possible to determine how processes will actually be scheduled. Efficient program analysis is therefore difficult as all process schedulings must be considered. To overcome this problem, we introduce a confluent semantics which closely approximates the standard (nonconfluent) semantics. This semantics provides a basis for efficient and accurate program analysis for these languages. To illustrate the usefulness of this approach, we sketch analyses based on abstract interpretations of the confluent semantics which determine if a program is suspension-and local suspension-free. @ Elsevier Science Inc., 1997 <I 1. INTRODUCTION Concurrent constraint logic programming [24, 26] is a programming paradigm based on logic programming with mechanisms for concurrency. In recent years, there has

Proceedings of the 12th international ACM SIGPLAN symposium on Principles and practice of declarative programming - PPDP '10, 2010

The Constraint Simplification Rules (CSR) subset of CHR and the flat subset of LCC, where agent nesting is restricted, are very close syntactically and semantically. The first contribution of this paper is to provide translations between CSR and flat-LCC. The second contribution is a transformation from the full LCC language to flat-LCC which preserves semantics. This transformation is similar to λ-lifting in functional languages. In conjunction with the equivalence between CHR and CSR with respect to original operational semantics, these results lead to semantics-preserving translations from full LCC to CHR and conversely. Immediate consequences of this work include new proofs for CHR linear logic and phase semantics, relying on corresponding results for LCC, plus an encoding of the λ-calculus in CHR. * A preliminary version of this work was presented at the CHR'09 workshop (informal proceedings). comparably to CHR constraints. Linear logic leads to a natural semantics for classical CC languages as well [8]. More recently, a precise declarative semantics for CHR has been described in linear logic [10]. Related work The translation from full LCC to CHR relies on ask-lifting. This is a transformation comparable to the λ-lifting [14] for functional languages: the common idea is the materialization of the environment in data structures, i.e. values in functional languages or tokens in LCC. The adaptations of functional concepts in LCC languages have been initiated with the embedding of closures and modules [13]. Flattening nested programming structures was suggested in [15] for connecting the Celf system [16] to CHR but no formal transformation seems to have been published. Encoding for RAM machines into CHR [29] showed that CHR was expressive enough to embed imperative style programming. The encoding of λ-calculus and closures shows that CHR can as well host programs written in a functional style. The CHR linear-logic semantics [10] is close to the previous work on the LCC semantics [8]: the present paper formally describes the intuitions behind this transposition.

ACM Computing Surveys, 1996

Theoretical Computer Science, 1997

Confluence is an important and desirable property as it allows the program to be understood by considering any desired scheduling rule, rather than having to consider all possible schedulings. Unfortunately, the usual operational semantics for concurrent constraint programs is not confluent as different process schedulings give rise to different sets of possible outcomes. We show that it is possible to give a natural confluent calculus for concurrent constraint programs, if the syntactic domain is extended by a blind choice operator and a special constant standing for a discarded branch. This has application to program analysis.

The Journal of Logic Programming, 1998

The Constraint Logic Programming (CLP) Scheme was introduced by Jaar and Lassez. The scheme gave a formal framework, based on constraints, for the basic operational, logical and algebraic semantics of an extended class of logic programs. This paper presents for the ®rst time the semantic foundations of CLP in a self-contained and complete package. The main contributions are threefold. First, we extend the original conference paper by presenting de®nitions and basic semantic constructs from ®rst principles, giving new and complete proofs for the main lemmas. Importantly, we clarify which theorems depend on conditions such as solution compactness, satisfaction completeness and independence of constraints. Second, we generalize the original results to allow for incompleteness of the constraint solver. This is important since almost all CLP systems use an incomplete solver. Third, we give conditions on the (possibly incomplete) solver which ensure that the operational semantics is con¯uent, that is, has independence of literal scheduling.

IEEE Software, 1995

The principle behind concurrent logic programming is a set of processes which cooperate in monotonically constraining a global set of variables to particular values. Each process will have access to only some of the variables, and a process may bind a variable to a tuple containing further variables which may be bound later by other processes. This is a suitable model for a coordination language. In this paper we describe a type system which ensures the cooperation principle is never breached, and which makes clear through syntax the pattern of data flow in a concurrent logic program. This overcomes problems previously associated with the practical use of concurrent logic languages.

Lecture Notes in Computer Science, 1996

Concurrent constraint programming is a simple but powerful framework for computation based on four basic computational ideas: concurrency (multiple agents are simultaneously active), communication (they interact via the monotonic accumulation of constraints on shared variables), coordination (the presence or absence of information can guard evolution of an agent), and localization (each agent has access to only a finite, though dynamically varying, number of variables, and can create new variables on the fly). Unlike other foundational models of concurrency such as CCS, CSP, Petri nets and the -calculus, such flexibility is already made available within the context of determinate computation. This allows the development of a rich and tractable theory of concurrent processes within the context of which additional computational notion such as indeterminacy, reactivity, instantaneous interrupts and continuous (dense-time) autonomous evolution have been developed. We survey the development of some of these extensions and the relationships between their semantic models.

Journal of Logic Programming, 1998

The Constraint Logic Programming (CLP) Scheme was introduced by Jaar and Lassez. The scheme gave a formal framework, based on constraints, for the basic operational, logical and algebraic semantics of an extended class of logic programs. This paper presents for the ®rst time the semantic foundations of CLP in a self-contained and complete package. The main contributions are threefold. First, we extend the original conference paper by presenting de®nitions and basic semantic constructs from ®rst principles, giving new and complete proofs for the main lemmas. Importantly, we clarify which theorems depend on conditions such as solution compactness, satisfaction completeness and independence of constraints. Second, we generalize the original results to allow for incompleteness of the constraint solver. This is important since almost all CLP systems use an incomplete solver. Third, we give conditions on the (possibly incomplete) solver which ensure that the operational semantics is con¯uent, that is, has independence of literal scheduling. Ó 1998 Elsevier Science Inc. All rights reserved.

Information and Computation, 2001

In this paper we give a logical semantics for the class CC of concurrent constraint programming languages and for its extension LCC based on linear constraint systems. Besides the characterization in intuitionistic logic of the stores of CC computations, we show that both the stores and the successes of LCC computations can be characterized in intuitionistic linear logic. We illustrate the usefulness of these results by showing with examples how the phase semantics of linear logic can be used to give simple "semantical" proofs of safety properties of LCC programs.

Artificial Intelligence, 1999