We study two encodings of the asynchronous #-calculus with input-guarded choice into its choice-free fragment. One encoding is divergence-free, but refines the atomic commitment of choice into gradual commitment. The other preserves atomicity, but introduces divergence. The divergent encoding is fully abstract with respect to weak bisimulation, but the more natural divergence-free encoding is not. Instead, we show that it is fully abstract with respect to coupled simulation, a slightly coarser---but still coinductively defined---equivalence that does not enforce bisimilarity of internal branching decisions. The correctness proofs for the two choice encodings introduce a novel proof technique exploiting the properties of explicit decodings from translations to source terms.

The asynchronous pi-calculus is considered the basis of experimental programming languages (or proposal of programming languages) like Pict, Join, and Blue calculus. However, at a closer inspection, these languages are based on an even simpler calculus, called Local (L), where: (a) only the output capability of names may be transmitted; (b) there is no matching or similar constructs for testing equality between names. We study the basic operational and algebraic theory of Lpi. We focus on bisimulation-based behavioural equivalences, precisely on barbed congruence. We prove two coinductive characterisations of barbed congruence in Lpi, and some basic algebraic laws. We then show applications of this theory, including: the derivability of delayed input; the correctness of an optimisation of the encoding of call-by-name lambda-calculus; the validity of some laws for Join.

We formulate a typed formalism for concurrency where types denote freely composable structure of dyadic interaction in the symmetric scheme. The resulting calculus is a typed reconstruction of name passing process calculi. Systems with both the explicit and implicit typing disciplines, where types form a simple hierarchy of types, are presented, which are proved to be in accordance with each other. A typed variant of bisimilarity is formulated and it is shown that typed fi-equality has a clean embedding in the bisimilarity. Name reference structure induced by the simple hierarchy of types is studied, which fully characterises the typable terms in the set of untyped terms. It turns out that the name reference structure results in the deadlock-free property for a subset of terms with a certain regular structure, showing behavioural significance of the simple type discipline. 1 Introduction This is a preliminary study of types for concurrency. Types here denote freely composable structur...

We study reduction congruence, a popular notion of process equality, for the asynchronous π-calculus with timers, and derive several alternative characterisations, one of them being a labelled asynchronous bisimilarity. These results are adapted to an asynchronous π-calculus with timers, locations and message failure. In addition we investigate the problem of how to distribute value-passing processes in a semantics-preserving way.

A possible analogue of theory of combinators in the setting of concurrent processes is formulated. The new combinators are derived from the analysis of the operation called asynchronous name passing, just as the analysis of logical substitution gave rise to the sequential combinators. A system with seven atoms and fixed interaction rules, but with no notion of prefixing, is introduced, and is shown to be capable of representing input and output prefixes over arbitrary terms in a behaviourally correct way, just as SK-combinators are closed under functional abstraction without having it as a proper syntactic construct. The basic equational correspondence between concurrent combinators and a system of asynchronous mobile processes, as well as the embedding of the finite part of ß-calculus in concurrent combinators, is proved. These results will hopefully serve as a cornerstone for further investigation of the theoretical as well as pragmatic possibilities of the presented construction. 1 ...

We compare the first-order and the higher-order...

this article that directly depends on the locality restriction imposed on the -calculus.

We give a labeled characterization of barbed congruence in asynchronous -calculus, which, unlike previous characterizations, does not use the matching construct. In absence of matching the observer cannot directly distinguish two names. In asynchronous -calculus the fact that two names are indistinguishable can be modeled by means of Honda and Yoshida's notion of equator. Our labeled characterization is based on such a notion. As an application of our theory we provide a fully abstract encoding w.r.t. barbed congruence of external mobility (communication of free names) in terms of internal mobility (communication of private names).

This paper introduces an operational semantics for call-by-need reduction in terms of Milner's ß-calculus. The functional programming interest lies in the use of ß-calculus as an abstract yet realistic target language. The practical value of the encoding is demonstrated with an outline for a parallel code generator. From a theoretical perspective, the ß-calculus representation of computational strategies with shared reductions is novel and solves a problem posed by Milner [13]. The compactness of the process calculus presentation makes it interesting as an alternative definition of call-by-need. Correctness of the encoding is proved with respect to the call-by-need -calculus of Ariola et al. [3]. 1 Introduction Graph reduction of extended -calculi has become a mature field of applied research. The efficiency of the implementations is due in great measure to a technique known as `sharing', whereby argument values are computed (at most) once and then memoized for future reference. Both...

The Blue Calculus is a direct extension of both the lambda and the pi calculi. In a preliminary work from Gérard Boudol, a simple type system was given that incorporates Curry's type inference for the lambda-calculus. In the present paper we study an implicit polymorphic type system, adapted from the ML typing discipline. Our typing system enjoys subject reduction and principal type properties and we give results on the complexity for the type inference problem. These are interesting results for the blue calculus as a programming notation for higher-order concurrency.