An Operational Semantics for Declarative Multi-Paradigm Languages

In this paper we define an operational semantics for functional logic languages covering notions like laziness, sharing, concurrency, non-determinism, etc. Such a semantics is not only important to provide appropriate language definitions to reason about programs and check the correctness of implementations but it is also a basis to develop languagespecific tools, like program tracers, profilers, optimizers, etc. First, we define a “big-step” semantics in natural style to relate expressions and their evaluated results. Since this semantics is not sufficient to cover concurrency, search strategies, or to reason about costs associated to particular computations, we also define a “small-step” operational semantics covering the features of modern functional logic languages.