Direct semantics of concurrent languages in the SMoLCS approach

For years providing syntax-directed methods for the formal definition of concurrent languages has proved to be a challenging task. Problems are even more difficult if a language has some of the typical Ada features, such as strong interference between sequential and concurrent aspects, parameterized semantics, complex data structure, and finally an extremely large size. We have developed an approach, the SMoLCS approach, which extends the denotational method to handle concurrent languages and also provides a solution to the above problems. Indeed, our method has been adopted for the format definition of full Ada within the related EEC project. Here we illustrate the basic principles of the approach, following the so-called direct semantics style used for Ada with the help of a toy language as a running example.