Professor Sir Charles Antony Richard Hoare FBCS has died at the age of 92. He is remembered as one of computer science and software engineering’s founding contributors. BCS would like to offer its condolences to Professor Hoare’s friends and family .
Martin Cooper MBCS reports, with contributions from Emeritus Professor Mark Woodman, a former undergraduate student of Tony Hoare’s, and Emeritus Professor David Bustard, a former doctoral student and researcher at QUB, and author in the professor’s famous series. ‘Tony changed our lives’, they both say.
Tony Hoare is remembered as one of computer science’s global founders, a British beacon, and as a man whose wry wit matched his mathematical and computing prowess. His work shaped the history of computing as we know and approach it today. Among a great many accolades, Tony received the Turing Award in 1980 for 'fundamental contributions to the definition and design of programming languages', and in 2023 was awarded the British Royal Society's Royal Medal for 'groundbreaking contributions that have revolutionised the computer programming field'.
Professor Dame Sue Black FBCS OBE, founder of BCS Women said: ‘I first met Tony when I was doing my PhD... I was very much in awe of him. We subsequently met… over the following years as part of the BCS FACS group… My condolences to his family and friends.’
Professor Dame Muffy Calder FREng FRSE FBCS FIEE said: ‘Tony Hoare was an extraordinary man who was one of the founders of theoretical computer science. I attended the Marktoberdorf summer school in 1981 where he gave a series of lectures on CSP… . I had never seen such elegance and clarity of thought. I will never forget him, or the event — they all changed my life.’
Tony is best known by programmers for creating Quicksort, the highly influential sorting algorithm he first devised in 1959 and which is still used today. He also introduced ‘Hoare logic’ in 1969, a foundational system for reasoning about program correctness, and he later developed communicating sequential processes (CSP), which shaped concurrent programming languages such as Occam and Erlang. He himself implemented a compiler for the seminal language Algol 60, a project on which he met his wife Jill Pym, a pioneer of women in computing. With Niklaus Wirth he developed Algol-W, a predecessor of Pascal and its many successors.
Tony’s wit
Along with his pioneering and foundational work, Tony also leaves some wonderful, droll and timeless quotes about the business of making software.
In BCS’ Computer Bulletin (December 1975), Tony wrote an article reflecting on what it might mean to be a software engineer: ‘The basic tools of the programmer are the programming languages and compilers, job control languages and operating systems, utilities and other software… But what a sorry comparison with the tools of other professions! That they are unreliable, that they are inconvenient in operation — these are facts that have been long recognised and widely suffered. Perhaps the worst symptom (and also a large part of the cause of the trouble) is their extraordinary and still increasing complexity, which totally beggars the comprehension of both user and designer.’
This aligns with another famous observation: ‘There are two ways of constructing a software design: one way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult.’
Early years
Tony Hoare was born on 11 January 1934 in Colombo and was educated in England. His first degree — possibly accentuating his gift for words — was Greats (Classics and Philosophy) at Merton College, Oxford.
After graduating, he joined the Royal Navy for his national service. There, he was trained in Russian. He returned to Oxford to complete a postgraduate certificate in statistics. This is when he learned to program.
Next, he went as an exchange student to Moscow State University. There, he studied under Andrey Kolmogorov, a pioneer of axiomatic foundations of probability theory. The work involved looking up words in a dictionary and it was this that led him to devise the now-famous Quicksort algorithm. He wrote it with paper and pencil while reclining on a couch! Then he worked at Elliott Brothers, a small London computer manufacturing firm. In 1968, Queens University Belfast took a remarkable risk in appointing someone from industry as Professor of Computing Science. After nine years he returned to Oxford as the Professor of Computing to lead the Programming Research Group, a veritable cauldron of essential computing,
What is Quicksort?
The algorithm was first published in a brief note in 1961 and in a detailed paper in 1962 by Elliott Brothers, also carried by BCS in the Computer Bulletin, in January 1962.
The paper’s introduction read: ‘A description is given of a new method of sorting in the random access store [RAM] of a computer. The method compares very favourably with other known methods in speed, in economy of storage, and in ease of programming. Certain refinements of the method, which may be useful in the optimisation of inner loops, are described…’
Over the years, Quicksort has been extensively cited and studied, and adapted for various computing environments like parallel systems and GPUs. Tony’s own further work on Quicksort with M. Foley (1971) provided formal proof of correctness. It’s stayed influential because this simple ‘split and sort the smaller bits’ idea turns out to be fast, efficient, and surprisingly elegant — versions of it still power sorting inside many programming languages today.
Besides algorithms, Hoare also made seminal contributions to programming languages, earning the 1980 Turing Award. His Turing paper The Emperor's Old Clothes echoes his perennial plea for simplicity.
Legacy
Tony Hoare left behind an enormous legacy, most of which is online. As if his own work was not enough, he founded and was the first series editor of the Prentice Hall International Series in Computer Science, which represents the best from the 20th century. The 50th book of that series, Essays in Computing Science (1989), is Tony Hoare’s own work, wonderfully edited by Professor Cliff Jones, and includes many Hoare classics. A PDF of the book is available.
After retiring from Oxford University, Tony became a senior principal researcher (1999–2015) at Microsoft Research, where he continued to publish and receive awards. The BCS FACS group celebrated his 90th birthday in 2024 by publishing a special newsletter to mark the occasion (available online).
Other memories
Santosh Shrivastava , Emeritus Professor and Senior Research Investigator Newcastle University recounts: ‘Tony Hoare was my ‘unofficial’ PhD supervisor… at Cambridge, [my supervisor] Maurice Wilkes… put me in touch with Dijkstra and Hoare. Hoare suggested that I do an implementation study of various synchronisation techniques… looking back, it took the combined efforts of three Turing laureates to push me through a PhD!’
Professor Sir Charles Antony Richard Hoare, or Tony Hoare as he remains fondly known, is survived by his wife of 64 years, Lady Jill Hoare and their children Tom and Joanna. Their son Matthew died in 1982.
BCS honours him and thanks him.
