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Pict: A programming language based on the picalculus
 PROOF, LANGUAGE AND INTERACTION: ESSAYS IN HONOUR OF ROBIN MILNER
, 1997
"... The πcalculus offers an attractive basis for concurrent programming. It is small, elegant, and well studied, and supports (via simple encodings) a wide range of highlevel constructs including data structures, higherorder functional programming, concurrent control structures, and objects. Moreover ..."
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Cited by 285 (9 self)
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The πcalculus offers an attractive basis for concurrent programming. It is small, elegant, and well studied, and supports (via simple encodings) a wide range of highlevel constructs including data structures, higherorder functional programming, concurrent control structures, and objects. Moreover, familiar type systems for the calculus have direct counterparts in the πcalculus, yielding strong, static typing for a highlevel language using the πcalculus as its core. This paper describes Pict, a stronglytyped concurrent programming language constructed in terms of an explicitlytypedcalculus core language.
A Foundation for Actor Computation
 Journal of Functional Programming
, 1998
"... We present an actor language which is an extension of a simple functional language, and provide a precise operational semantics for this extension. Actor configurations represent open distributed systems, by which we mean that the specification of an actor system explicitly takes into account the in ..."
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Cited by 259 (52 self)
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We present an actor language which is an extension of a simple functional language, and provide a precise operational semantics for this extension. Actor configurations represent open distributed systems, by which we mean that the specification of an actor system explicitly takes into account the interface with external components. We study the composability of such systems. We define and study various notions of testing equivalence on actor expressions and configurations. The model we develop provides fairness. An important result is that the three forms of equivalence, namely, convex, must, and may equivalences, collapse to two in the presence of fairness. We further develop methods for proving laws of equivalence and provide example proofs to illustrate our methodology.
An Interactionbased Language and its Typing System
 In PARLE’94, volume 817 of LNCS
, 1994
"... We present a small language L and its typing system based on the idea of interaction, one of the important notions in parallel and distributed computing. L is based on, apart from such constructs as parallel composition and process creation, three pairs of communication primitives which use the noti ..."
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Cited by 152 (21 self)
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We present a small language L and its typing system based on the idea of interaction, one of the important notions in parallel and distributed computing. L is based on, apart from such constructs as parallel composition and process creation, three pairs of communication primitives which use the notion of a session, a semantically atomic chain of communication actions which can interleave with other such chains freely, for highlevel abstraction of interactionbased computing. Three primitives enable programmers to elegantly describe complex interactions among processes with a rigorous type discipline similar to ML [4]. The language is given formal operational semantics and a type inference system, regarding which we prove that if a program is welltyped in the typing system, it never causes runtime error due to type inconsistent communication patterns, offering a new foundation for type discipline in parallel programming languages. 1 Introduction The idea of interaction, that is, rec...
A Concurrent Object Calculus: Reduction and Typing
 HLCL'98 TO APPEAR
, 1998
"... We obtain a new formalism for concurrent objectoriented languages by extending Abadi and Cardelli's imperative object calculus with operators for concurrency from thecalculus and with operators for synchronisation based on mutexes. Our syntax of terms is extremely expressive; in a precise sen ..."
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Cited by 84 (4 self)
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We obtain a new formalism for concurrent objectoriented languages by extending Abadi and Cardelli's imperative object calculus with operators for concurrency from thecalculus and with operators for synchronisation based on mutexes. Our syntax of terms is extremely expressive; in a precise sense it unifies notions of expression, process, store, thread, and configuration. We present a chemicalstyle reduction semantics, and prove it equivalent to a structural operational semantics. We identify a deterministic fragment that is closed under reduction and show that it includes the imperative object calculus. A collection of type systems for objectoriented constructs is at the heart of Abadi and Cardelli's work. We recast one of Abadi and Cardelli's firstorder type systems with object types and subtyping in the setting of our calculus and prove subject reduction. Since our syntax of terms includes both stores and running expressions, we avoid the need to separate store typing from typing of expressions. We translate asynchronous communication channels and the choicefree asynchronouscalculus into our calculus to illustrate its expressiveness; the types of readonly and writeonly channels are supertypes of readwrite channels.
Modular structural operational semantics
, 2004
"... Modular SOS (MSOS) is a variant of conventional Structural Operational Semantics (SOS). Using MSOS, the transition rules for each construct of a programming language can be given incrementally, once and for all, and do not need reformulation when further constructs are added to the language. MSOS th ..."
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Cited by 77 (8 self)
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Modular SOS (MSOS) is a variant of conventional Structural Operational Semantics (SOS). Using MSOS, the transition rules for each construct of a programming language can be given incrementally, once and for all, and do not need reformulation when further constructs are added to the language. MSOS thus provides an exceptionally high degree of modularity in language descriptions, removing a shortcoming of the original SOS framework. After sketching the background and reviewing the main features of SOS, the paper explains the crucial differences between SOS and MSOS, and illustrates how MSOS descriptions are written. It also discusses standard notions of semantic equivalence based on MSOS. Appendix A shows how the illustrative MSOS rules given in the paper would be formulated in conventional SOS.
A Calculus of Broadcasting Systems
 SCIENCE OF COMPUTER PROGRAMMING
, 1991
"... CBS is a simple and natural CCSlike calculus where processes speak one at a time and are heard instantaneously by all others. Speech is autonomous, contention between speakers being resolved nondeterministically, but hearing only happens when someone else speaks. Observationally meaningful laws dif ..."
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Cited by 75 (8 self)
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CBS is a simple and natural CCSlike calculus where processes speak one at a time and are heard instantaneously by all others. Speech is autonomous, contention between speakers being resolved nondeterministically, but hearing only happens when someone else speaks. Observationally meaningful laws differ from those of CCS. The change from handshake communication in CCS to broadcast in CBS permits several advances. (1) Priority, which attaches only to autonomous actions, is simply added to CBS in contrast to CCS, where such actions are the result of communication. (2) A CBS simulator runs a process by returning a list of values it broadcasts. This permits a powerful combination, CBS with the host language. It yields several elegant algorithms. Only processes with a unique response to each input are needed in practice, so weak bisimulation is a congruence. (3) CBS subsystems are interfaced by translators; by mapping messages to silence, these can restrict hearing and hide speech. Reversi...
HigherOrder Concurrent Programs with Finite Communication Topology (Extended Abstract)
, 1994
"... Concurrent ML (CML) is an extension of the functional language Standard ML (SML) with primitives for the dynamic creation of processes and channels and for the communication of values over channels. Because of the powerful abstraction mechanisms the communication topology of a given program may be v ..."
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Cited by 66 (11 self)
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Concurrent ML (CML) is an extension of the functional language Standard ML (SML) with primitives for the dynamic creation of processes and channels and for the communication of values over channels. Because of the powerful abstraction mechanisms the communication topology of a given program may be very complex and therefore an efficient implementation may be facilitated by knowledge of the topology. This paper presents an analysis for determining when a bounded number of processes and channels will be generated. The analysis proceeds in two stages. First we extend a polymorphic type system for SML to deduce not only the type of CML programs but also their communication behaviour expressed as terms in a new process algebra. Next we develop an analysis that given the communication behaviour predicts the number of processes and channels required...
NonInterleaving Semantics for Mobile Processes
 Theoretical Computer Science
, 1995
"... This paper studies causality in ßcalculus. Our notion of causality combines the dependencies given by the syntactic structure of processes with those originated by passing names. Our studies show that two transitions not causally related may however occur in a fixed ordering in any computation, i.e ..."
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Cited by 43 (19 self)
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This paper studies causality in ßcalculus. Our notion of causality combines the dependencies given by the syntactic structure of processes with those originated by passing names. Our studies show that two transitions not causally related may however occur in a fixed ordering in any computation, i.e., ßcalculus may implicitly express a precedence between actions. Our causality relation still induces the same partial order of transitions for all the computations that are obtained by shuffling transitions that are concurrent (i.e. related neither by causality nor by precedence). Other noninterleaving semantics are investigated and compared. The presentation takes advantage from a parametric definition of process behaviour given in an SOS style. All the results on bisimulationbased equivalences, congruences, axiomatizations and logics are taken (almost) without modifications from the interleaving theory. Finally, we extend our approach to higherorder ßcalculus, enriched with a spawn ...
A Theory of Weak Bisimulation for Core CML
 J. Functional Programming
, 1993
"... Concurrent ML (CML) is an extension of Standard ML of New Jersey with concurrent features similar to those of process algebra. In this paper, we build upon John Reppy's reduction semantics for CML by constructing a compositional operational semantics for a fragment of CML, basedon higherorder p ..."
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Cited by 41 (9 self)
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Concurrent ML (CML) is an extension of Standard ML of New Jersey with concurrent features similar to those of process algebra. In this paper, we build upon John Reppy's reduction semantics for CML by constructing a compositional operational semantics for a fragment of CML, basedon higherorder process algebra. Using the operational semantics we generalise the notion of weak bisimulation equivalence to build a semantic theory of CML. We give some small examples of proofs about CML expressions, and show that our semantics corresponds to Reppy's up to weak firstorder bisimulation. 1 Introduction There have been various attempts to extend standard programming languages with concurrent or distributed features, (Giacalone et al., 1989; Holmstrom, 1983; Nikhil, 1990). Concurrent ML (CML) (Reppy, 1991a; Reppy, 1992; Panangaden & Reppy, 1996) is a practical and elegant example. The language Standard ML is extended with two new type constructors, one for generating communication channels, and t...
Concurrent ML: Design, Application and Semantics
, 1993
"... Machine" [BB90], except that there are no "cooling" and "heating" transitions (the process sets of this semantics can be thought of as perpetually "hot" solutions). The concurrent evaluation relation extends "7\Gamma!" to finite sets of terms (i.e., proce ..."
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Cited by 41 (0 self)
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Machine" [BB90], except that there are no "cooling" and "heating" transitions (the process sets of this semantics can be thought of as perpetually "hot" solutions). The concurrent evaluation relation extends "7\Gamma!" to finite sets of terms (i.e., processes) and adds additional rules for process creation, channel creation, and communication. We assume a set of process identifiers, and define the set of processes and process sets as: ß 2 ProcId process IDs p = hß; ei 2 Proc = (ProcId \Theta Exp) processes P 2 Fin(Proc) process sets We often write a process as hß; E[e]i, where the evaluation context serves the role of the program counter, marking the current state of evaluation. Definition4. A process set P is wellformed if for all hß; ei 2 P the following hold:  FV(e) = ; (e is closed), and  there is no e 0 6= e, such that hß; e 0 i 2 P. It is occasionally useful to view wellformed process sets as finite maps from ProcId to Exp. If P is a finite set of process state...