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.

We present a set of concurrency primitives for Standard ML. We define these by giving the transitional semantics of a simple language. We prove that our semantics preserves the expected behaviour of sequential programs. We also show that we can define stores as processes, such that the representation has the same behaviour as a direct definition. These proofs are the first steps towards integrating our semantics with the full definition of Standard ML. 1 Background and Motivation There have been several attempts to add concurrency primitives to Standard ML (SML) and related languages [Hol83, Mat91, Rep91a, CM90, Ber89]. However, when we began this work none of these implementations had a published formal definition. The formal definition of SML is an integral part of the development of the language. If we are to add concurrency to the language, it is essential that we have a formal semantics for the new constructs that is compatible with the existing definition. In this paper we prese...

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 well-formed 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 well-formed process sets as finite maps from ProcId to Exp. If P is a finite set of process state...

This paper describes eXene, a user interface toolkit implemented in a concurrent extension of Standard ML. The design and use of eXene is inextricably woven with the presence of multiple threads and a high-level language. These features replace the object-oriented design of most toolkits, and provide a better basis for dealing with the complexities of user interfaces, especially concerning such aspects as type safety, extensibility, component reuse and the balance between the user interface and other parts of the program. 1

Recent attempts at incorporating concurrency into functional languages have identified synchronous communication via shared channels as a promising primitive. An additional useful feature found in many proposals is a nondeterministic choice operator. Similar in nature to the CSP alternative command, this operator allows different possible actions to be guarded by sends or receives. Choice is difficult to implement in a distributed environment because it requires offering many potential communications but closing only one. In this paper we present the first distributed, deadlock-free algorithm for choice. Keywords: Distributed protocols, channels, synchronous communication, choice operator, CSP alternative command. 1. Introduction In 1978, C.A.R. Hoare introduced a now-classic paradigm for parallel programming called communicating sequential processes, or CSP [12]. CSP presented a new approach to concurrent programming, and its legacy has continued to influence wellfounded pr...

This paper is about the recently-developed framework of action semantics.

This research is an attempt to reason about the control of parallel computation in the world of applicative programming languages. Applicative languages, in which computation is performed through function application and in which functions are treated as first-class objects, have the benefits of elegance, expressiveness and having clean semantics. Parallel computation and real-world concurrent activities are much harder to reason about than the sequential counterparts. Many parallel applicative languages have thus hidden most control details with their declarative programming styles, but they are not expressive enough to characterize many real world concurrent activities that can be easily explained with concepts such as message passing, pipelining and so on. Ease of programming should not come at the expense of expressiveness. Therefore, we design a parallel applicative language Pscheme such that programmers can express explicitly the control of parallel computation while maintaining ...

The Machine-Assisted Proof of Programming Language Properties Myra VanInwegen Advisor: Carl Gunter The goals of the project described in this thesis are twofold. First, we wanted to demonstrate that if a programming language has a semantics that is complete and rigorous (mathematical), but not too complex, then substantial theorems can be proved about it. Second, we wanted to assess the utility of using an automated theorem prover to aid in such proofs. We chose SML as the language about which to prove theorems: it has a published semantics that is complete and rigorous, and while not exactly simple, is comprehensible. We encoded the semantics of Core SML into the theorem prover HOL (creating new definitional packages for HOL in the process). We proved important theorems about evaluation and about the type system. We also proved the type preservation theorem, which relates evaluation and typing, for a good portion of the language. We were not able to complete the proof of type prese...

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