His work on automata theory earned him the ACM Turing Award in 1976, while his collaborative work with Christopher Strachey in the 1970s laid the foundations of modern approaches to the semantics of programming languages.
O seu traballo sobre a teoría de autómatas fíxoo merecedor do Premio Turing da ACM en 1976, mentres que o seu traballo en colaboración con Christopher Strachey nos anos 1970 fixaron as bases para os enfoques modernos en semántica de linguaxes de programación.