A personal perspective

This book has its origins in my interest in semantics and logics for locality in programming languages. By locality, I mean the various mechanisms that exist for making local declarations, restricting a resource to a specific scope, or hiding information from the environment. Although mathematics and logic are involved in understanding these things, this is a distinctively computer science topic. I was introduced to it by Matthew Hennessy and Alley Stoughton when we all arrived at the University of Sussex in the second half of the 1980s. At the time I was interested in applying category theory and logic to computer science and they were interested in the properties of the mixture of local mutable state and higher-order functions that occurs in the ML family of languages (Milner et al., 1997).

Around that time Moggi introduced the use of category-theoretic monads to structure different notions of computational effect (Moggi, 1991). That is now an important technique in denotational semantics; and thanks to the work of Wadler (1992) and others, monads are the accepted way of ‘tackling the awkward squad’ (Peyton Jones, 2001) of side-effects within functional programming. One of Moggi's monads models the computational effect of dynamically allocating fresh names. It is less well known than some of the other monads he uses, because it needs categories of functors and is only mentioned in (Moggi, 1989), rather than (Moggi, 1991).