Maude MSOS tool Modular structural operational semantics (MSOS) is a new framework that allows structural operational semantics (SOS) specifications to be made modular in the sense of not imposing the redefinition of transition rules, which is the case in SOS specifications, when an extension is made. Maude MSOS tool (MMT) is an executable environment for MSOS implemented in Full Maude as a realization of a semantics-preserving mapping between MSOS and rewriting logic (RWL). The modular SOS definition formalism (MSDF) is the specification language supported by MMT. MSDF syntax is quite close to MSOS mathematical notation and user-friendly by allowing several syntactic components to be left implicit. MMT joins the support for modularity with a user-friendly syntax together with the efficient execution and analysis of the Maude engine. We have used MMT in several different examples from programming languages semantics and concurrent systems. This paper reports on the development of MMT and its application to these two classes of specifications.

This software is also peer reviewed by journal TOMS.