Observational Semantics for a Concurrent Lambda Calculus with Reference Cells and Futures

International audienceWe present an observational semantics for lambda(fut), a concurrent lambda calculus with reference cells and futures. The calculus lambda(fut) models the operational semantics of the concurrent higher-order programming language Alice ML. Our result is a powerful notion of equivalence that is the coarsest nontrivial congruence distinguishing observably different processes. It justifies a maximal set of correct program transformations, and it includes all of lambda(fut)'s deterministic reduction rules, in particular, call-by-value beta reduction

Characterizing contextual equivalence in calculi with passivation

AbstractWe study the problem of characterizing contextual equivalence in higher-order languages with passivation. To overcome the difficulties arising in the proof of congruence of candidate bisimilarities, we introduce a new form of labeled transition semantics together with its associated notion of bisimulation, which we call complementary semantics. Complementary semantics allows to apply the well-known Howeʼs method for proving the congruence of bisimilarities in a higher-order setting, even in the presence of an early form of bisimulation. We use complementary semantics to provide a coinductive characterization of contextual equivalence in the HOπP calculus, an extension of the higher-order π-calculus with passivation, obtaining the first result of this kind. We then study the problem of defining a more effective variant of bisimilarity that still characterizes contextual equivalence, along the lines of Sangiorgiʼs notion of normal bisimilarity. We provide partial results on this difficult problem: we show that a large class of test processes cannot be used to derive a normal bisimilarity in HOπP, but we show that a form of normal bisimilarity can be defined for HOπP without restriction

A theory of bisimulation for a fragment of concurrent ML with local names.

Concurrent ML is an extension of Standard ML with π-calculus-like primitives for multi-threaded programming. CML has a reduction semantics, but to date there has been no labelled transitions semantics provided for the entire language. We present a labelled transition semantics for a fragment of CML called μvCML which includes features not covered before: dynamically generated local channels and thread identifiers. We show that weak bisimulation for μvCML is a congruence, and coincides with barbed bisimulation congruence. We also provide a variant of D. Sangiorgi's (1993) normal bisimulation for μvCML, and show that this too coincides with bisimulation

A theory of bisimulation for a fragment of concurrent ML with local names

Concurrent ML is an extension of Standard ML with ?-calculus-like primitives for multithreaded programming. CML has a reduction semantics, but to date there has been no labelled transition system semantics provided for the entire language. In this paper, we present a labelled transition semantics for a fragment of CML called µvCML which includes features not covered before: dynamically generated local channels and thread identifiers. We show that weak bisimilarity for µvCML is a congruence, and coincides with barbed bisimulation congruence. We also provide a variant of Sangiorgi's normal bisimulation for µvCML, and show that this too coincides with bisimilarity

A theory of bisimulation for a fragment of concurrent ML with local names

Concurrent ML is an extension of Standard ML with p-calculus-like primitives for multi-threaded programming. CML has a reduction semantics, but to date there has been no labelled transitions semantics provided for the entire language. In this paper, we present a labelled transition semantics for a fragment of CML called nCML which includes features not covered before: dynamically generated local channels and thread identifiers. We show that weak bisimilarity for nCML is a congruence, and coincides with barbed bisimulation congruence. We also provide a variant of Sangiorgi's normal bisimulation for nCML, and show that this too coincides with bisimilarity