Scala fuses object-oriented and functional programming in a statically typed programming language. It is aimed at the construction of components and component systems. This paper gives an overview of the Scala language for readers who are familar with programming methods and programming language design.

We identify three programming language abstractions for the construction of reusable components: abstract type members, explicit selftypes, and modular mixin composition. Together, these abstractions enable us to transform an arbitrary assembly of static program parts with hard references between them into a system of reusable components. The transformation maintains the structure of the original system. We demonstrate this approach in two case studies, a subject/observer framework and a compiler front-end.

9706572, and the US Air Force under grant F19628-95-C-0050 and a generous fellowship. The views and conclusions contained in this document are those of the author and should not be interpreted as representing the official policies, either expressed or implied, of any sponsoring institution, the U.S. government or any other entity.

One promising approach for adding object-oriented (OO) facilities to functional languages like ML is to generalize the existing datatype and function constructs to be hierarchical and extensible, so that datatype variants simulate classes and function cases simulate methods. This approach allows existing datatypes to be easily extended with both new operations and new variants, resolving a longstanding conflict between the functional and OO styles. However, previous designs based on this approach have been forced to give up modular typechecking, requiring whole-program checks to ensure type safety. We describe Extensible ML (EML), an ML-like language that supports hierarchical, extensible datatypes and functions while preserving purely modular typechecking. To achieve this result, EML’s type system imposes a few requirements on datatype and function extensibility, but EML is still able to express both traditional functional and OO idioms. We have formalized a core version of EML and proven the associated type system sound, and we have developed a prototype

Component-based programming is currently carried out using mainstream object-oriented languages. These languages have to be used in a highly disciplined way to guarantee flexible component composition and extensibility. This paper investigates abstractions for component-oriented programming on the programming language level. We propose a simple prototype-based model for first-class components on top of a class-based object-oriented language. The model is formalized as an extension of Featherweight Java. Our calculus includes a minimal set of primitives to dynamically build, extend, and compose software components, while supporting features like explicit context dependencies, late composition, unanticipated component extensibility, and strong encapsulation. We present a type system for our calculus that ensures type-safe component definition, composition, and evolution.

Abstract. This paper formalizes and proves correct a compilation scheme for mutually-recursive definitions in call-by-value functional languages. This scheme supports a wider range of recursive definitions than standard call-by-value recursive definitions. We formalize our technique as a translation scheme to a lambda-calculus featuring in-place update of memory blocks, and prove the translation to be faithful.

We present the programming language Keris, an extension of Java with explicit support for software evolution. Keris introduces extensible modules as the basic building blocks for software. Modules are composed hierarchically revealing explicitly the architecture of systems. A distinct feature of the module design is that modules do not get linked manually. Instead, the wiring of modules gets infered. The module assembly and refinement mechanism of Keris is not restricted to the unanticipated extensibility of atomic modules. It also allows to extend fully linked systems by replacing selected submodules with compatible versions without needing to re-link the full system. Extensibility is type-safe and non-invasive; i.e. the extension of a module preserves the original version and does not require access to source code.

This paper proposes an operational semantics for value recursion in the context of monadic metalanguages. Our technique for combining value recursion with computational effects works uniformly for all monads. The operational nature of our approach is related to the implementation of recursion in Scheme and its monadic version proposed by Friedman and Sabry, but it defines a different semantics and does not rely on assignments. When contrasted to the axiomatic approach proposed by Erkök and Launchbury, our semantics for the continuation monad invalidates one of the axioms, adding to the evidence that this axiom is problematic in the presence of continuations. 1

We define a calculus for investigating the interactions between mixin modules and computational effects, by combining the purely functional mixin calculus CMS with a monadic metalanguage supporting the two separate notions of simplification (local rewrite rules) and computation (global evaluation able to modify the store). This distinction is important for smoothly integrating the CMS rules (which are all local) with the rules dealing with the imperative features. In our calculus mixins...

Mixin modules are a framework for modular programming that supports code parameterization, incremental programming via late binding and redefinitions, and cross-module recursion. In this paper, we develop a language of mixin modules that supports call-by-value evaluation, and formalize a reduction semantics and a sound type system for this language.