The language Esterel has found success in many safety-critical applications, such as fly-by-wire systems and nuclear power plant control software. Its imperative style is natural to programmers building such systems and its precise semantics makes it work well for reasoning about programs. Existing semantics of Esterel generally fall into two categories: translation to Boolean circuits, or operational semantics that give a procedure for running a whole program. In contrast, equational theories enable reasoning about program behavior via equational rewrites at the source level. Such theories form the basis for proofs of transformations inside compilers or for program refactorings, and defining program evaluation syntactically. This paper presents the first such equational calculus for Esterel. It also illustrates the calculus’s usefulness with a series of example equivalences and discuss how it enabled us to find bugs in Esterel implementations.

Exceptions are invaluable for structured error handling in high-level languages, but they are at odds with linear types. More generally, control effects may delete or duplicate portions of the stack, which, if we are not careful, can invalidate all substructural usage guarantees for values on the stack. We have developed a type-and-effect system that tracks control effects and ensures that values on the stack are never wrongly duplicated or dropped. We present the system first with abstract control effects and prove its soundness. We then give examples of three instantiations with particular control effects, including exceptions and delimited continuations, and show that they meet the soundness criteria for specific control effects.

Alms is a general-purpose programming language that supports practical affine types. To offer the expressiveness of Girard's linear logic while keeping the type system light and convenient, Alms uses expressive kinds that minimize notation while maximizing polymorphism between affine and unlimited types.

We describe an implementation of session types in Haskell. Session types statically enforce that client-server communication proceeds according to protocols. They have been added to several concurrent calculi, but few implementations of session types are available.