SAVCBS 2003: Specification and Verification of Component-Based Systems

These are the proceedings for the SAVCBS 2003 workshop. This workshop was held at ESEC/FSE 2003 in Helsinki Finland in September 2003

Effect handlers via generalised continuations

Plotkin and Pretnar's effect handlers offer a versatile abstraction for modular programming with user-defined effects. This paper focuses on foundations for implementing effect handlers, for the three different kinds of effect handlers that have been proposed in the literature: deep, shallow, and parameterised. Traditional deep handlers are defined by folds over computation trees, and are the original construct proposed by Plotkin and Pretnar. Shallow handlers are defined by case splits (rather than folds) over computation trees. Parameterised handlers are deep handlers extended with a state value that is threaded through the folds over computation trees. We formulate the extensions both directly and via encodings in terms of deep handlers, and illustrate how the direct implementations avoid the generation of unnecessary closures. We give two distinct foundational implementations of all the kinds of handlers we consider: a continuation passing style (CPS) transformation and a CEK-style abstract machine. In both cases, the key ingredient is a generalisation of the notion of continuation to accommodate stacks of effect handlers. We obtain our CPS translation through a series of refinements as follows. We begin with a first-order CPS translation into untyped lambda calculus which manages a stack of continuations and handlers as a curried sequence of arguments. We then refine the initial CPS translation by uncurrying it to yield a properly tail-recursive translation, and then moving towards more and more intensional representations of continuations in order to support different kinds of effect handlers. Finally, we make the translation higher-order in order to contract administrative redexes at translation time. Our abstract machine design then uses the same generalised continuation representation as the CPS translation. We have implemented both the abstract machine and the CPS transformation (plus extensions) as backends for the Links web programming language

Acute: high-level programming language design for distributed computation

Existing languages provide good support for typeful programming of standalone programs. In a distributed system, however, there may be interaction between multiple instances of many distinct programs, sharing some (but not necessarily all) of their module structure, and with some instances rebuilt with new versions of certain modules as time goes on. In this paper we discuss programming language support for such systems, focussing on their typing and naming issues. We describe an experimental language, Acute, which extends an ML core to support distributed development, deployment, and execution, allowing type-safe interaction between separately-built programs. The main features are: (1) type-safe marshalling of arbitrary values; (2) type names that are generated (freshly and by hashing) to ensure that type equality tests suffice to protect the invariants of abstract types, across the entire distributed system; (3) expression-level names generated to ensure that name equality tests suffice for type-safety of associated values, e.g. values carried on named channels; (4) controlled dynamic rebinding of marshalled values to local resources; and (5) thunkification of threads and mutexes to support computation mobility. These features are a large part of what is needed for typeful distributed programming. They are a relatively lightweight extension of ML, should be efficiently implementable, and are expressive enough to enable a wide variety of distributed infrastructure layers to be written as simple library code above the byte-string network and persistent store APIs. This disentangles the language runtime from communication intricacies. This paper highlights the main design choices in Acute. It is supported by a full language definition (of typing, compilation, and operational semantics), by a prototype implementation, and by example distribution libraries

S.IM.PL Serialization: Type System Scopes Encapsulate Cross-Language, Multi-Format Information Binding

Representing data outside of and between programs is important in software that stores, shares, and manipulates information. Formats for representing information, varying from human-readable verbose (XML) to light-weight, concise (JSON), and non-human-readable formats (TLV) have been developed and used by applications based on their data and communication requirements. Writing correct programs that produce information represented in these formats is a difficult and time-consuming task, as developers must write repetitive, tedious code to map loosely-typed serialized data to strongly-typed program objects. We developed S.IM.PL Serialization, a cross-language multi-format information binding framework to relieve developers from the burdens associated with the serialization of strongly-typed data structures. We developed type system scopes, a means of encapsulating data types and binding semantics as a cross-language abstract semantics graph. In comparison to representing data binding semantics and information structure through external forms such as schemas, configuration files, and interface description languages, type system scopes can be automatically generated from declarations in a data binding annotation language, facilitating software engineering. Validation is based on use in research applications, a study of how computer science graduate students use the software to develop applications, and performance benchmarks. As a case study, we also examine the cross-language development of a Team Coordination (TeC) game

Modular, higher order cardinality analysis in theory and practice

Since the mid '80s, compiler writers for functional languages (especially lazy ones) have been writing papers about identifying and exploiting thunks and lambdas that are used only once. However, it has proved difficult to achieve both power and simplicity in practice. In this paper, we describe a new, modular analysis for a higher order language, which is both simple and effective. We prove the analysis sound with respect to a standard call-by-need semantics, and present measurements of its use in a full-scale, state-of-the-art optimising compiler. The analysis finds many single-entry thunks and one-shot lambdas and enables a number of program optimisations. This paper extends our preceding conference publication (Sergey et al. 2014 Proceedings of the 41st Annual ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages (POPL 2014). ACM, pp. 335–348) with proofs, expanded report on evaluation and a detailed examination of the factors causing the loss of precision in the analysis