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In Memoriam | doi:10.1145/1743546.1743556 Leah Hoffmann Robin Milner: The Elegant Pragmatist Remembering a rich legacy in verification, languages, and concurrency.

tam c e as a surprise even to programmed to cooperate on a single those who knew him well: the task. CCS was succeeded by a more death of Arthur John Robin “Robin initiated a general theory of concurrency called pi Gorell Milner, known to friends revolution in what calculus, which incorporated dynamic simply as Robin, of a heart at- computing languages generation, and , a theory of Itack on March 20. Milner’s wife, Lucy, ubiquitous computing. For his work on had died three weeks before. Yet the pi- are and could be,” LCF, ML, and CCS, Milner received the oneering computer scientist remained ACM A.M. in 1991. active, and seemingly in good health, says Robert Harper. “Robin had this ability to think until the end, maintaining close con- large and translate that all the way nections with his colleagues and even down to new theorems,” says Mads co-authoring a paper with a postdoc- Tofte, vice chancellor of the IT Univer- toral student he supervised at the IT sity of Copenhagen and a former grad- University of Copenhagen. uate student. The sentiment is echoed A man of modest background and Functions (LCF), an interactive sys- by many of Milner’s collaborators, quiet brilliance, Milner made ground- tem that helps researchers formulate who cite his unfailing ability to shift breaking contributions to the fields of proofs. “It was a novel idea,” says Robert from a grand vision of computing to verification, programming languages, Harper, a professor of subtle mathematical particulars. Cou- and concurrency. He was born in 1934 at Carnegie Mellon University. “The ap- pled with his rigorous attention to de- near Plymouth, , and won proach before then was that computers tail, the trait gave Milner’s work a firm scholarships to Eton—where he devel- would search for your proof. Robin rec- grounding in practical applications. oped an enduring love of math as well ognized that the computer is a tool to “He was very concerned with making as a prodigious work ethic—and King’s help you find the proof.” During that re- things work,” says , a College, . It was during his search, Milner also laid the foundations former colleague at the University of time at Cambridge that Milner was in- of ML, a metalanguage whose original Edinburgh. troduced to programming, though the intent was to enable researchers to de- Milner also labored on behalf of in- subject didn’t interest him initially. “I ploy proof tactics on LCF. The innovative stitutions and initiatives that shaped regarded programming as really rather concepts it introduced, however—such the future of the field. He helped es- inelegant,” he recalled in an interview as polymorphic type inference and type- tablish the Laboratory for Foundations in 2001 with Martin Berger, a profes- safe exception handling—were soon of Computer Science at the University sor at the University of Sussex. “So I recognized. Ultimately, ML evolved into of Edinburgh and served as the first resolved that I would never go near a powerful general programming lan- chair of the ’s a computer in my life.” Several years guage (with Milner, Harper, and others Computer Laboratory. In 2002, Milner later, in 1960, Milner broke that resolu- working to specify and standardize it) and , a senior researcher at tion with a programming job at Ferran- and led to languages like F# and Caml. Microsoft Research in Cambridge (and ti, a British computer company; from “Robin initiated a revolution in a fellow Turing Award winner), began there, it wasn’t long before he moved to what computing languages are and working on a grand challenge initiative academia with positions at City Univer- could be,” asserts Harper. to identify research topics that would sity London, , Stan- Although he was closely involved drive science in the 21st century. ford University, and the Universities of in ML’s development throughout the He was a natural leader, according to Edinburgh and Cambridge. 1980s and 1990s, Milner also began Tofte. “I’m not sure he was always aware Inspired by ’s famous working on the problem of concur- of it,” says Tofte, “but he was so good at a v E

formulation of domain theory, Milner rency, looking for a mathematical getting the best out of people, which is d n a

l began working on an automatic theo- treatment that could rival theories of exactly what a good leader does.” rem prover, hoping to find a way to sequential computation. The Calcu- by Ro

Leah Hoffmann is a Brooklyn, NY-based technology

aph mechanize a logic for reasoning about lus of Communicating Systems (CCS) r writer. o

t programs. The work culminated in the was the first solution he devised: a pro- o h P g development of Logic for Computable cess calculus for a network that was © 2010 ACM 0001-0782/10/0600 $10.00

june 2010 | vol. 53 | no. 6 | communications of the acm 21