Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In 1st International Symposium on Object Technologies for Advanced Software, volume 472 of LNCS, pages 460--474. Springer-Verlag, November 1993. 21  Home/Search   Document Details and Download   Summary   Related Articles   Check

....Consider, for example EDp ( CCFM01] where we use a construct which represent atomic transactions as a mean to model e services. Interaction between a client and a server takes place only if both parties agree on a set of service parameters. The second example is the calculus of objects (CO) of [VT93], upon which the TyCO programming language is based ( Vas94] It models distributed object systems where messages are dispatched to a certain object if and only if it provides the method invoked in the request, and it is ready to execute it. Its semantics requires agreement on both object ....

V. T. Vasconcelos and M. Tokoro. A typing system for a calculus of objects. In Object Technologies for Advanced Software, volume 742 of LNCS, pages 460--474. Springer-Verlag, November 1993.

....is to dynamically check for message not understood errors. A process knows the messages it can (immediately) handle and if a received message does not conform to this interface, it raises a message not understood error (see the initial actor model [1] or the Vasconcelos and Tokoro object calculus [26]) But this approach reduces consequently the set of programs that one may build. In fact, the programmer must adopt a sort of synchronous programming discipline to be sure that messages arrive in right states. We think that this strategy is too restrictive. For example, consider a printer device ....

V. T. Vasconcelos and M. Tokoro. A typing system for a calculus of objects. In Proc. of OTAS, Kanazawa, Japan, volume 742 of LNCS, pages 460-474, New York, USA, 1993. Springer-Verlag.

....The second problem is to model a distributed object system where messages are dispatched to a certain object if and only if it provides the method invoked in the request, and it is ready to execute it. An accomplished solution is the semantics of Vasconcelos and Tokoro s calculus of objects [31], upon which the TyCO programming language is based [30,26] The first problem requires interaction to take place only if both customer and service provider agree on a set of service parameters. The second one requires the message and the recipient to agree on object identity and method. Both ....

Vasconcelos, V. T. and M. Tokoro, A typing system for a calculus of objects, in: Object Technologies for Advanced Software, LNCS 742, Springer-Verlag, 1993 pp. 460--474.

....the Imperative and Functional Object Calculi for instance, their discriminating power and to prove properties about them, within a single framework. The type language we use for the calculus is taken from [21, 24] In these type systems, as well as other type systems for the calculus like [12, 28, 9], types are assigned to names. The types in [21] show the arity and the directionality of a name and, recursively, of the names carried by that name; the di erence in [24] is variant types in place of tupling. All values are simple , in the sense that they are built out of names only, and cannot ....

V. Vasconcelos and M. Tokoro. A typing system for a calculus of objects. In Proc. Object Technologies for Advanced Software `93, volume 742 of Lecture Notes in Computer Science, pages 460-474. Springer Verlag, 1993.

....in which actors and asynchronous communications are primitives [7] This calculus has been designed with the aim of studying type inference for actor based languages. For this purpose we took inspiration in existing concurrent calculus: Milner s calculus [12] Vasconcelos concurrent objects [15] and Cardelli s primitive objects [1] Our experience in implementing actors [11] lead us to think that the ability for an actor to capture its own address (ego) and its own behavior (self) are important to formalize this model. For this purpose we have extended the self application mechanism of ....

....Aux Join Creation s a b c d m(x d) reply(v) Serv s c The server s before duplication : The server s after duplication : 3 Current works on types We have defined this calculus to study the problem of type inference systems for actors. At the moment our approach is still close to [15] and [10] in the sense that the types we associate to actors are object types. But the actors we want to type don t behave as objects in the sense that they can completely change their behavior: change their method definition and their interface. Our first proposition (developed in [6] is to ....

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Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In Proceedings of the International Symposium on Object Technologies for Advanced Software, LNCS 742, pages 460--474. Springer-Verlag, November 1993. 7

.... a) always able to handle requests to the same set of methods, and b) always accessible (each method can be handled any number of times) This hypothesis allows the use of type systems designed for sequential object oriented languages (either kind based ones as proposed by Vasconcelos and Tokoro [VT93] and by Kobayashi and Yonezawa [KY94] or subtype based ones as advocated by the authors in [CPS97] The rst step in this work, presented in [CPS97] consisted in de ning a set based analysis for uniform behavior concurrent objects (using a attening operation for merging all possible behaviors ....

.... (t v ) get (hreply 1 (t v )i)i. The parameter of get must be able to handle one reply message holding the value of type t v which has been put in the bu er. Usual type systems for concurrent object would only provide the following type hput(t v ) get(hreply(t v )i)i (see Vasconcelos [VT93] Kobayashi [KY94] or [CPS97] Exemple 3.2 (Linear cell) The following storage cell is linear in the sense that it is empty initially, can be written once and then can be read forever: let full cell ( val ) behavior message get ( c ) send reply( val ) to c end; let empty cell ( behavior ....

Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In Proceedings of the International Symposium on Object Technologies for Advanced Software, LNCS 742, pages 460-474. Springer-Verlag, November 1993.

.... is a) always able to handle requests to the same set of methods, and b) always accessible (each method can be handled any number of times) This hypothesis allows the use of type systems designed for sequential object oriented languages (either kind based ones as proposed by Vasconcelos and Tokoro [VT93] and by Kobayashi and Yonezawa [KY94] or subtype based ones as advocated by the authors in [CPS97b] In the case of objects with non uniform behavior (i.e. short lifetime objects or behavior changing actors) an object may be able to handle a request to one of its method at a given time and not ....

....Therefore, the typing of encoded programs generally lead to type information which do not reflect the structure of the original program. In previous work on typing objects and actors, Vasconcelos et al. advocated the use of an extension of the asynchronous calculus with record like objects (see [VT93]) Their calculus relies on replication in order to express the recursive structure of objects. As actors can change their behavior when they handle a message, their behaviors are defined as mutually recursive object structures. The replication based encoding of mutually recursive structures ....

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Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In Proceedings of the International Symposium on Object Technologies for Advanced Software, LNCS 742, pages 460--474. Springer-Verlag, November 1993.

....deadlocks and are not the goal of this paper (apart from their semantic characterization) we concentrate on the static detection of safety orphans. Type systems for concurrent objects and actors, with uniform or non uniform behaviors, have been the subject of active research in the last years ( VAS 93] NIE 95] KOB 94] KOB 95] PUN 96] NAJ 97] RAV 97] FOU 97] DAL 97] and their more recent works) Two opposite approaches have been followed: explicit and implicit typing. Explicit types may provide more precise information but are sometimes very hard to write for the programmer ....

....value which is not a message . and a first kind of concurrent errors related to communication: arity mismatch between a message and its target behavior. These errors, denoted Err, correspond to the usual ones in concurrent calculi (see [MIL 91] BOU 97] and [FOU 96] in concurrent objects ( VAS 93] or in actors ( KOB 94] The second kind of concurrent errors is related to the absence of communications: orphan messages. Such messages will not be treated by their target and will stay indefinitively in the communication medium. In the context of objects, orphan messages correspond to the ....

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VASCONCELOS V. T., TOKORO M., "A typing system for a calculus of objects", Proc. of ISOTAS, LNCS 742, Springer-Verlag, Nov.

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Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In 1st International Symposium on Object Technologies for Advanced Software, volume 472 of LNCS, pages 460--474. Springer-Verlag, November 1993. 21

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Vasconcelos V. and Tokoro M. A Typing System for a Calculus of Objects. In International Symposium on Object Technologies for Advanced Software (ISOTAS'93), volume 742 of LNCS, pages 460--474. Springer-Verlag, November 1993.

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Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In 1st International Symposium on Object Technologies for Advanced Software, volume 472 of LNCS, pages 460--474. Springer-Verlag, November 1993. 20

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Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In Proc. of ISOTAS'93, LNCS 742, pages 460--474. Springer-Verlag, 1993.

....a discipline in the usage of the programming language constructors that not only provides for partial correctness, but also helps in writing clear programs. Furthermore, a type for a program often gives some indication on the correct usage of the program. The calculus of concurrent objects [28] aims at capturing fundamental notions present in concurrent objects. Programs are built from names and labels by means of a few constructors, namely: asynchronous labelled messages, objects composed of collections of labelled methods, concurrent composition, and an operator enabling to create a ....

.... message invocation) and instantiation not possible (wrong number of arguments in a process instantiation) Inspired on the calculus [13, 10] and on the actor model of computation [2, 9] T yCO (TYped Concurrent Objects) grows from the basic calculus of objects and its monomorphic type system [28], by introducing recursive types [5, 27] process abstractions, and predicative polymorphism [6, 24] This constitutes what we call core T yCO. We then introduce a notion of expressions to be incorporated in the core calculus. Expressions simplify the writing of programs by hiding communication ....

[Article contains additional citation context not shown here]

Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In 1st ISOTAS, volume 742 of LNCS, pages 460--474. Springer-Verlag, November 1993.

....formulation due to Honda and Tokoro [11, 20] and Boudol [6] has been the starting point for most of these attempts. Several forms and extensions of the asynchronous calculus have since been proposed to provide for more direct programming styles, and to improve efficiency and expressiveness [7, 9, 32]. Dataflow and von Neumann architectures represent the two extremes in a continuous design space. In the dataflow model, computations are triggered by the availability of all input values to an instruction (the firing rule) This makes the model totally asynchronous and the instructions self ....

....a shift driven by Nikhil and Arvind s seminal work on P RISC [22] Languages that allow an efficient compilation from highlevel constructs into low level, fine grained, threads are quite suitable for multithreaded computing. In this context, there are several advantages in using process calculi [9, 11, 32] for concurrent and parallel computing. Process calculi provide a natural programming model as they deal with the notions of communication and concurrency. They usually have very small kernel calculi, with well understood semantics that form ideal frameworks for language implementations. This ....

[Article contains additional citation context not shown here]

V. Vasconcelos and M. Tokoro. A Typing System for a Calculus of Objects. In International Symposium on Object Technologies for Advanced Software (ISOTAS'93), volume 742 of LNCS, pages 460--474. Springer-Verlag, 1993.

....thus enforcing some kind of typing discipline on the usage of channels [14, 21, 19] Recently, a considerable effort has been devoted to the problem of introducing objects into these calculi [8, 20, 24] thus providing a formal framework for modeling concurrent object oriented languages. TyCO [20, 22] is just one of these efforts. It is a calculus that formally describes the 2 concurrent interaction of ephemeral objects through asynchronous communication. The calculus grows from the polyadic calculus and its monomorphic type system, by introducing recursive types, a polymorphic type system ....

....is just one of these efforts. It is a calculus that formally describes the 2 concurrent interaction of ephemeral objects through asynchronous communication. The calculus grows from the polyadic calculus and its monomorphic type system, by introducing recursive types, a polymorphic type system [22], templates and variables over templates. Synchronous communication can be achieved as usual by incorporating in messages an extra name intended to convey the result of the communication. The fundamental entities of the calculus are messages and ephemeral objects. Templates are specifications of ....

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V. Vasconcelos and M. Tokoro. A Typing System for a Calculus of Objects. In 1st International Symposium on Object Technologies for Advanced Software, LNCS, volume 742, pages 460--474. SpringerVerlag, November 1993. 21

....is an asynchronous version of the calculus. The calculus turns out to be a subcalculus of that preserves its computational power. 2. Nierstrasz de nes OC [Nie92] a calculus of objects that uni es and calculi, supporting communication of tuples of terms; 3. Vasconcelos de nes T yCO [VT93] Typed Concurrent Objects, a name passing object calculus with asynchronous communication. The calculus is an extension of the asynchronous calculus with input guarded labelled sums denoting methods in objects, and labelled asynchronous messages that select a branch of the sum. The aim of the ....

....or because it will never have the right method for the message. 2.1 Aims To ensure program safety, that is, the absence of run time errors, a popular approach is the use of a static type system. Traditional type systems assign rigid interface like types to the names of the objects [Mil93, VT93, KY95] We adopt a behaviours as types approach, such that a type is able to characterise all possible life cycles of an object, thus providing information about possible sequences of interactions. Types are terms of a process algebra, namely higher order labelled transition systems, which ....

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Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In Proceedings of the 1st International Symposium on Object Technologies for Advanced Software, volume 742 of Lecture Notes in Computer Science, pages 460-474. Springer-Verlag, 1993.

....is usually the case of liveness properties) Thus, the types should capture the flow of the processes, being themselves processes [Bou98, GH99, HVK98, IK01, Kob00, Yos96] Note that some of these systems assign types to processes, not to names. In a name passing calculus of objects such as T yCO [VT93] or # V a [San98] processes denote the behaviour of a community of interacting objects, where each object has a location identified by a name. Statically detecting method not understood errors is a more delicate problem in systems of (possibly distributed) concurrent objects. The usual ....

Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In Proceedings of the 1st International Symposium on Object Technologies for Advanced Software, volume 742 of Lecture Notes in Computer Science, pages 460--474. Springer-Verlag, 1993.

.... Walker s calculus or an equivalent asynchronous formulation due to Honda and Tokoro has been the starting point for most of these attempts [9, 17] In this paper we use Vasconcelos Typed Concurrent Objects to de ne a strongly typed, polymorphic, concurrent, object oriented language named TyCO [23, 25]. Typed Concurrent Objects is a form of the asynchronous calculus featuring rst class objects, asynchronous messages, and template de nitions. The calculus formally describes the concurrent interaction of ephemeral objects through asynchronous communication. Synchronous communication can be ....

....on a sequence of variables allowing, for example, for classes to be modeled. 2 Lopes, Silva and Vasconcelos Unbounded behavior is modeled through explicit instantiation of recursive templates. A type system assigns monomorphic types to variables and polymorphic types to template variables [25]. Other type systems have been proposed that support non uniform object interfaces [20] The calculus is reminiscent of the Abadi and Cardelli s calculus in the sense that objects are sums of labeled methods attached to names, the self parameters, and messages can be seen as asynchronous method ....

[Article contains additional citation context not shown here]

V. Vasconcelos and M. Tokoro. A Typing System for a Calculus of Objects. In 1st International Symposium on Object Technologies for Advanced Software, LNCS, volume 742, pages 460-474. Springer-Verlag, November 1993.

....the future. The paper presents a type system that is able to type objects with a non uniform service availability, while preserving the subject reduction property. An extended and revised version of a paper presented at Euro Par 97. 1 A typical process not typable by traditional type systems [VH93, VT93, KY95, LW95] is a one place buffer that only allows read operations when it is full, and write operations when it is empty. Empty(b) b B [ write : u) Full(b u) Full(b u) b B [ read : r) r C val : u] j Empty(b) The type systems mentioned above assign interface like types to names. Therefore, name ....

....not be considered an error, for the presence of a message b C write : u] makes the reception of the read message possible. The development of a type system able to type processes like the one above is the main motivation of this work. 2 The calculus of objects TyCO (TYped Concurrent Objects) [VT93, Vas94] is an object oriented name passing calculus with asynchronous communication between concurrent objects via labelled messages carrying names. The calculus is developed along the trends of well known models of concurrency, such as the calculus [Mil91, MPW92] the calculus [HT91] and the actor ....

[Article contains additional citation context not shown here]

V. Vasconcelos and M. Tokoro. A typing system for a calculus of objects. In 1st International Symposium on Object Technologies for Advanced Software, volume LNCS 742, pages 460--474. Springer-Verlag, 1993.

....Core T yCO Appendix to the Language Definition, yielding Version 0.2 Vasco T. Vasconcelos July 2001 This is the third report on T yCO [2] a (still) experimental strongly and implicitly typed concurrent object based programming language based on a predicative polymorphic calculus of objects [1, 3], featuring asynchronous messages, objects, and procedures, together with a predicative polymorphic typing assignment system, assigning monomorphic types to variables and polymorphic types to procedures. With respect to version 0.2, version 0.3 introduces 1. slight changes to the concrete syntax, ....

Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In 1st International Symposium on Object Technologies for Advanced Software, volume 472 of LNCS, pages 460--474. Springer-Verlag, November 1993. 3

....inter platform support in heterogeneous networks by using emulated byte code for implementation technology, much like Java RMI. Distributed TyCO DiTyCO, the model and system architecture we propose in this paper, is based on a form of the calculus called Typed Concurrent Objects TyCO [24]. The model features, first class objects, asynchronous method invocations, and class definitions. The calculus formally describes the concurrent interaction of ephemeral objects through asynchronous communication. Synchronous communication is implemented by sending continuations in messages. ....

....The focus of this paper is on the extension of the T yCO process calculus and its language implementation to support distribution and code mobility. However, the main ideas that support this work can be easily embodied in any namepassing calculus that satisfies a few mild pre conditions (e.g. [4, 11, 12, 17, 24]) T yCO [24] Typed Concurrent Objects) is a namepassing calculus in the line of the asynchronous calculus [11] that uses labeled asynchronous messages and objects composed of methods as the fundamental processes. Messages and objects are prefixed by names that represent their locations. In ....

[Article contains additional citation context not shown here]

V. Vasconcelos and M. Tokoro. A Typing System for a Calculus of Objects. In ISOTAS'93, LNCS 742, 460--474, Springer-Verlag, 1993.

....inter platform support in heterogeneous networks by using emulated byte code for implementation technology, much like Java RMI. Distributed TyCO DiTyCO, the model and system architecture we propose in this paper, is based on a form of the calculus called Typed Concurrent Objects TyCO [24]. The model features, first class objects, asynchronous method invocations, and class definitions. The calculus formally describes the concurrent interaction of ephemeral objects through asynchronous communication. Synchronous communication is implemented by sending continuations in messages. ....

....The focus of this paper is on the extension of the T yCO process calculus and its language implementation to support distribution and code mobility. However, the main ideas that support this work can be easily embodied in any namepassing calculus that satisfies a few mild pre conditions (e.g. [4, 11, 12, 17, 24]) T yCO [24] Typed Concurrent Objects) is a namepassing calculus in the line of the asynchronous calculus [11] that uses labeled asynchronous messages and objects composed of methods as the fundamental processes. Messages and objects are prefixed by names that represent their locations. In ....

[Article contains additional citation context not shown here]

V. Vasconcelos and M. Tokoro. A Typing System for a Calculus of Objects. In ISOTAS'93, LNCS 742, 460--474, Springer-Verlag, 1993.

....formulation due to Honda and Tokoro [11, 20] and Boudol [6] has been the starting point for most of these attempts. Several forms and extensions of the asynchronous calculus have since been proposed to provide for more direct programming styles, and to improve efficiency and expressiveness [7, 9, 32]. Dataflow and von Neumann architectures represent the two extremes in a continuous design space. In the dataflow model, computations are triggered by the availability of all input values to an instruction (the firing rule) This makes the model totally asynchronous and the instructions self ....

....a shift driven by Nikhil and Arvind s seminal work on P RISC [22] Languages that allow an efficient compilation from highlevel constructs into low level, fine grained, threads are quite suitable for multithreaded computing. In this context, there are several advantages in using process calculi [9, 11, 32] for concurrent and parallel computing. Pro cess calculi provide a natural programming model as they deal with the notions of communication and concurrency. They usually have very small kernel calculi, with well understood semantics that form ideal frameworks for language implementations. This ....

[Article contains additional citation context not shown here]

V. Vasconcelos and M. Tokoro. A Typing System for a Calculus of Objects. In International Symposium on Object Technologies for Advanced Software (ISOTAS'93), volume 742 of LNCS, pages 460--474. Springer-Verlag, 1993.

.... polyadic calculus [8] Honda s calculus [6, 7] and Hewitt s actor model [5] we developed a calculus intended to capture basic features present in most notions of objects, and to give precise (operational) semantics and type inference systems to object oriented concurrent programming languages [14]. The calculus is built along the trends of name passing calculi, by introducing labelled sums representing methods, and asynchronous labelled messages selecting a branch in a sum. A type system assigns types to the free names in (untyped) terms, specifying in some sense the communication protocol ....

....free names in (untyped) terms, specifying in some sense the communication protocol of the term, and ensuring that objects in well typed programs do not receive messages for which they do not possess an appropriate method. The present paper consolidates the presentation of the calculus of objects [14], and introduces an extension to the basic type system to accommodate recursive types. Recursive types, of the form t:ff for t a type variable and ff an arbitrary type, are interpreted In Transactions of Information Processing Society of Japan, 35(9) 1828 1836, September 1994. 1 as (possibly ....

[Article contains additional citation context not shown here]

Vasco T. Vasconcelos and Mario Tokoro. A typing system for a calculus of objects. In 1st International Symposium on Object Technologies for Advanced Software, volume 742 of LNCS, pages 460--474. Springer-Verlag, November 1993.

....calculus setting such as T yCO [10] processes denote the behaviour of a community of interacting objects, where each object has a location identified by a name. Each process determines an assignment of types to names reflecting a discipline for communication. The usual types as records paradigm [11] gives each name a static type that contains information about all the methods of the object, regardless of whether they are enabled or not. Hereby we propose an algebra of object types, where each type is essentially a collection of enabled methods, and it is dynamic in the sense that the ....

V. Vasconcelos and M. Tokoro. A typing system for a calculus of objects. In 1st International Symposium on Object Technologies for Advanced Software, volume LNCS 742, pages 460--474. SpringerVerlag, 1993. 6

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