The keyword revolution

Abstract

An ongoing trend is to develop new mechanisms for composing software modules that resemble the relations between corresponding problem-domain entities and thus enable a natural decomposition of software for an increasing number of problem domains. However, we have observed that today's programming languages hard-wire a fixed set of composition mechanisms, usually in terms of keywords. To overcome this limitation, we have proposed the Co-op approach enabling developers to implement an open-ended number of composition mechanisms as first-class citizens. Extending our previous prototype which focused on the composition of behavior, this paper reports on our prototype Co-op/II which facilitates implementing composition mechanisms for data access. We show that our approach is sufficient to realize several styles, e.g., of sharing data between sub classes, of controlling visibility, and of behavioral modifiers like synchronization of data access, converting or persisting data. PROBLEM STATEMENTTo be able to properly decompose a software system into modules which correspond to the entities of the problem domain, sufficient mechanisms must be provided to compose the modules into a running system again. There is a continuous trend [10] in software engineering research to develop programming languages with composition mechanisms that map to relations between problem-domain entities. Thus a natural decomposition of software is enabled for an increasing number of problem domains. The key to these composition mechanisms is abstraction: Program elements can use others without explicitly referring to their implementation; typically, multiple implementations of an abstraction exist and the execution environment selects one according to well-defined rules.A popular example of a composition mechanism is inheritance, where the behavior of a child class is composed with the behavior of the parent. Already for this well known example, many different variants exist [11]. Examples of other Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee.

Reuse of continuation-based control-flow abstractions

“…To overcome the complexity brought by CPS, C# 5 introduces the keywords async and await to achieve asynchronous computations. 5 For ECMAScript extended with generators, which adds the keyword yield to the language, the same is achieved as library functions. 6 Several unified implementation techniques are discussed in literature, which, however, are limited to modeling a request-reply-style of composition rather than arbitrary control flow composition as presented in this paper.…”

“…A composition mechanism may involve several semantic concerns; previously, we have explored behavior-related concerns, expressing different behavioral compositions such as inheritance, delegation, and aspects [12], and we explored data-related concerns, expressing varying semantics for e.g. data sharing and visibility [5]. In this paper, we focus on the control flow related semantics of compositions.…”