Functional Active Objects: Typing and Formalisation

This paper provides a sound foundation for autonomous objects communicating by remote method invocations and futures. As a distributed extension of sigma-calculus, we define aspfun, a calculus of functional objects, behaving autonomously and communicating by a request-reply mechanism: requests are method calls handled asynchronously and futures represent awaited results for requests. This results in a well structured distributed object language enabling a concise representation of asynchronous method invocations. This paper first presents the aspfun calculus and its semantics. Secondly we provide a type system for aspfun, which guarantees the ``progress'' property. Most importantly, aspfun and its properties have been formalised and proved using the Isabelle theorem prover, and we consider it as a good step toward formalisation of distributed languages.