|Born||5 June 1930|
|Died||3 June 2009(aged 78)|
|Known for||ISWIM, J operator, SECD machine, off-side rule|
Peter John Landin (5 June 1930, Sheffield – 3 June 2009) was a British computer scientist. He was one of the first to realize that the lambda calculus could be used to model a programming language, an insight that is essential to development of both functional programming and denotational semantics.
Landin was born in Sheffield, where he attended King Edward VII School; he graduated from Clare College, Cambridge University. From 1960 to 1964, he was the assistant to Christopher Strachey when the latter was an independent computer consultant in London. Most of his work was published during this period and the brief time he worked for Univac and at the Massachusetts Institute of Technology in the United States before taking a position at Queen Mary, University of London. During the 1970s and 1980s, his efforts went into building the Computer Science department in Queen Mary College, developing courses and teaching students. On his retirement, he was appointed Emeritus Professor of Theoretical Computation at Queen Mary, University of London, where the Computer Science building was renamed in 2012 to Peter Landin Building in his honour.
At a workshop at the Science Museum, London, in 2001, on the history of programming semantics he spoke of how his scholarly career in computer science began in the late 1950s and of how he was much influenced by a study of McCarthy's LISP when the most commonly used language was Fortran.
He was active in the definition of the ALGOL programming language and cited by Tony Hoare as one of the people who taught him ALGOL 60 and hence facilitated his expression of powerful recursive algorithms:
"Around Easter 1961, a course on ALGOL 60 was offered in Brighton, England, with Peter Naur, Edsger W. Dijkstra, and Peter Landin as tutors. ... It was there that I first learned about recursive procedures and saw how to program the sorting method which I had earlier found such difficulty in explaining. It was there that I wrote the procedure, immodestly named QUICKSORT, on which my career as a computer scientist is founded. Due credit must be paid to the genius of the designers of ALGOL 60 who included recursion in their language and enabled me to describe my invention so elegantly to the world. I have regarded it as the highest goal of programming language design to enable good ideas to be elegantly expressed."
Landin is responsible for inventing the SECD machine, the first abstract process virtual machine ever defined, and the ISWIM programming language, defining the Landin off-side rule and for coining the term syntactic sugar. The off-side rule allows bounding scope declaration by use of white spaces as seen in languages such as Miranda, Haskell, Python and F# (using the "light" syntax).
Another phrase originating with Landin is "The next 700 ..." after his influential paper The next 700 programming languages. "700" was chosen because Landin had read in the Journal of the ACM that there were already 700 programming languages in existence. The paper opens with the quotation "... today ... 1,700 special programming languages used to 'communicate' in over 700 application areas." It also includes the joke that
a reference to his earlier paper. This dry sense of humour is expressed in many of his papers.
Landin, who was bisexual, became involved with the Gay Liberation Front (GLF) during the early 1970s. He was once arrested as part of an anti-nuclear demonstration. He was a dedicated cyclist and moved around London on his bike until it became physically impossible for him to do so.
Selected publications 
- Landin, Peter J. (1964). "The mechanical evaluation of expressions". The Computer Journal (British Computer Society) 6 (4): 308–320.
- Landin, Peter J. (1966). "A formal description of Algol 60". In T. B. Steel, Jr. Formal Language Description Languages for Computer Programming: 266–294.
- Landin, Peter J. (February 1965a). "Correspondence between ALGOL 60 and Church's Lambda-notation: part I". Communications of the ACM (Association for Computing Machinery) 8 (2): 89–101.
- Landin, Peter J. (March 1965b). "A correspondence between ALGOL 60 and Church's Lambda-notation: part II". Communications of the ACM (Association for Computing Machinery) 8 (3): 158–165.
- Landin, Peter J. (29 August 1965). "A Generalization of Jumps and Labels". UNIVAC Systems Programming Research (technical report). Reprinted in Higher-Order and Symbolic Computation, 11, 125–143 (1998).
- Landin, Peter J. (March 1966). "The next 700 programming languages". Communications of the ACM (Association for Computing Machinery) 9 (3): 157–166. doi:10.1145/365230.365257.
See also 
- Peter Landin, Lambda the Ultimate, 4 June 2009.
- Bornat 2009a
- Acknowledged in the foreword to the text book Programming from First Principles by Richard Bornat. Published by Prentice Hall, 1987. ISBN 978-0-13-729104-5.
- Program Verification and Semantics: Report, 2001.
- Listed amongst those who attended the November 1959 conference in [Paris]  and the 1962 conference .
- Landin 1964b
- ACM Turing Award Lecture: The Emperor's Old Clothes. C. Antony R. Hoare, 1980, Published in the Communications of the ACM.
- Landin 1966
- Personal communication, September 2007.
- Computer Software Issues, an American Mathematical Association Prospectus, July 1965.
- Landin 1965a
- Bornat 2009b
Further reading 
- Bornat, Richard (23 September 2009). "Peter Landin obituary". The Guardian (Obituaries ed.): 34. Retrieved 29 September 2009.
- Bornat, Richard (17 September 2009). "Peter Landin: a computer scientist who inspired a generation, 5th June 1930 - 3rd June 2009". Formal Aspects of Computing (Berlin: Springer-Verlag) 21 (5): 393–395. doi:10.1007/s00165-009-0122-y. ISSN 0934-5043.
- List of publications from the DBLP Bibliography Server
- List of publications from Microsoft Academic Search
- Program Verification and Semantics: The Early Work, BCS Computer Conservation Society seminar, Science Museum, London, UK, 5 June 2001
- Memorial talk on Landin's life by Olivier Danvy at ICFP 2009
- Peter Landin's talk at Program Verification and Semantics: The Early Work, 2001 (video)