Declarative programming with algebra

Abstract

The Algebra of Communicating Processes (ACP) is a theory that views sequences and choices as mathematical operations: multiplication and addition. Based on these base constructs others are defined, such as parallel merge, interruption and disruption. Conventional programming languages may be enriched with ACP features, to gain declarative expressiveness. We have done this in SubScript, an extension to the Scala language. SubScript has high level support for sequences, choices and iterations in a style similar to parser generator languages. It also offers parallel composition operations, such as andand or- parallelism, and dataflow. The declarative style is also present in the way various execution modes are supported. Conventional programming languages often require some boilerplate code to run things in the background, in the GUI thread, or as event handlers. SubScript supports the same execution modes, but with minimal boilerplate. It is also easy to compose programs from blocks having different execution modes. This paper introduces ACP and SubScript; it briefly describes the current implementation, and gives several examples.