An Abstract Machine for Curry and Its Concurrent Implementation in Java

Curry is a multi-paradigm declarative language aiming to amalgamate functional, logic, and concurrent programming paradigms. Curry combines in a seamless way features from functional programming and (concurrent) logic programming. Curry’s operational semantics is based on the combination of lazy reduction of expressions together with a possibly non-deterministic binding of free variables occurring in expressions. Moreover, (equational) constraints can be executed concurrently which provides for passive constraints and concurrent computation threads that are synchronized on logical variables. This paper describes in an object-oriented style an abstract machine for executing Curry programs. The machine is designed to provide a link for compiling Curry programs into Java but it can also be a basis for implementations of Curry in other (object-oriented) languages. The main emphasis of the Java-based implementation is the exploitation of Java threads to implement the concurrent and nondeterministic features of Curry.