13 April 2023

Obituary for professor emeritus Neil Jones


Neil Deaton Jones, professor emeritus at DIKU, the Department of Computer Science at the University of Copenhagen, passed away Monday 27 March 2023, shortly after his 82nd birthday. He will be remembered for his seminal contributions to programming language research and theory of computation and for the impact his visions and his work have had on an entire generation of researchers, students and collaborators.

Neil Jones at DIKU's 40th anniversary in 2010
Neil Jones at DIKU's 40th anniversary in 2010

Obituary written by Fritz Henglein

Neil Deaton Jones was born 22 March, 1941, in Centralia, Illinois, to Neil Jones, a welder, and Serma Deaton Jones, a homemaker, far from the centers of university life and, as he would put it, as far from a coast as was possible in the United States. Early on he developed a keen interest and great talent for intellectual endeavors, frequently visiting the local library and devouring its contents. 

He paid his own way through college and graduate school by computer programming and receiving scholarships. He received a Bachelor’s degree in Mathematics from Southern Illinois University (1962), then a Master of Arts in Mathematics and Computing (1965) and a Doctor of Philosophy in Mathematics (1967) from the University of Western Ontario.

At age 26 he joined Penn State University as assistant professor (1967) where he was quickly promoted to associate professor (1969). He moved to the University of Kansas (1973) where he soon after, at age 34, was promoted to full professor (1975), a position he held until 1981. 

He was guest professor at Aarhus University (1976-77) while on leave from the University of Kansas. There something dramatic happened – we will get to that – which had him come back to Denmark, first as as visiting associate professor at Aarhus University (1979-81), then permanently as an associate professor (1982-87) and finally full professor at DIKU, a position he held until his transition to professor emeritus status (1987-2007).  He vigorously pursued research, the second love of his life, until January 2023, when he fell ill with COVID19, was hospitalized and passed away only two months later. 

Neil Jones has had a tremendous impact on computer science, uniquely combining deep theory with a programming (language) perspective. He contributed fundamental concepts and solutions to multiple subfields of computer science, and he worked tirelessly to improve the practice of programming by deep theoretical insights—and the theory of computation and programming languages guided by the practice of programming.  

Pioneer of programming-language methods

Neil was appointed Fellow of the Association of Computing Machinery (ACM) in 1998, received the Knight of the Dannebrog Order by the Queen of Denmark in 1998, was given the Alexander-von-Humboldt Award and Stipend in 2008, and was the recipient of the ACM SIGPLAN Programming Languages Achievement Award, the most prestigious recognition in programming language research, in 2014 for being “[..] a pioneer of programming-language methods. He introduced control-flow analysis for higher-order programs, binding-time analysis to tame self-applicable partial evaluation, what is known today as ‘Jones optimality’, and size-change termination analysis.

Neil is also noted for bridges he established between programming languages and complexity/computability theory, e.g., characterizing Turing's Universal Machine as self interpretation, Kleene's S-m-n theorem as partial evaluation, Kleene's second recursion theorem as reflection, and the expressive power of typed cons-free functional languages by means of complexity classes. His pioneering work on complexity theory included the development of completeness for P and solving the spectrum problem [...]. Lastly, Neil is a tireless and inspiring mentor, and he has written several influential textbooks that are testaments to his thesis that programs are data objects and that programming languages are a cornerstone of computer science.”  (Source: ACM SIGPLAN website).

Neil was a sought-after invited speaker and guest professor, with extended stays at INRIA, University of Paris, Ecole Normale Superieure, National University of Singapore, University of Oxford, Stanford Research Institute, Chalmers University and University of Freiburg. Conversely, he hosted more than twenty researchers from around the world spending sabbaticals, leaves and extended visits at DIKU. 

Human impact

At DIKU he founded the Theory and Practice of Programming Languages (abbreviated to TOPPS, from its Danish name) research group and invited students to join him in a daring endeavor: Making partial evaluation (also called program specialization or staged computation) not only self-applicable, but also practically efficient, an ambition that was considered beyond reasonable at the time. It succeeded and gave rise to an explosive interest in partial evaluation, especially after he brought together the pioneers of partial evaluation from around the world at the Partial Evaluation and Mixed Computation (PEMC) workshop at Gl. Avernæs in Denmark in 1987.  It spawned the still ongoing annual Partial Evaluation and Semantics-based Program Manipulation (PEPM) ACM symposium series.  

His visions, modest demeanor and generosity attracted many students that have become leaders in academia and industry themselves. His students and TOPPS alumni went on to hold professorships in the United States, Australia, Denmark, France, Sweden, Singapore, Germany; TOPPS alumni co-founded some of Denmark’s most successful IT enterprises, including a new university.  He was inclusive and collaborative – listing his collaborators on the achievements above would, while deserved, be a daunting task – and encouraged TOPPS members to develop and pursue their own research agendas, which included functional programming language design and implementation, region-based memory management, efficient type-based program analysis, constraint-based pointer analysis, reversible computing, novel mathematical models of programming languages and much more that was pioneered in the TOPPS group.

Love of his life

When an eager PhD graduate gatecrashed his office at DIKU in 1990 without an appointment, Neil immediately set up a visiting schedule for him, and when the graduate shortly afterwards confided that he was looking for a postdoc position in Copenhagen because of a Danish woman he had fallen in love with, Neil’s face lit up and he professed: “That’s why I am here!”  And he told the story of meeting the love of his life, his wife Lene, during his guest professorship at the University of Aarhus, which set him on a personal quest to come to Denmark.   

Neil is survived by his wife, Lene Rold, his daughter Katherine Jones Francis, his sister Lynn Moore, and two grandsons.  

He has moved on, but his scientific legacy as scientist, mentor and human will last forever. Rest In Peace, Neil.


Fritz Henglein
Department of Computer Science
University of Copenhagen 

Mads Tofte

DIKU Communication


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