Charles Leonard Hamblin

Inventor of Reverse Polish Notation and the stack in computing, Hamblin was an Australian philosopher, logician, and computer pioneer. He served as a professor of philosophy at the Technical University of New South Wales (now the University of New South Wales) in Sydney. Among his most well-known achievements in the area of computer science was the introduction (some sources also say invention) of Reverse Polish Notation and the invention of the stack in computing. This was arguably independent of and about the same time as the work of Friedrich Ludwig Bauer and Klaus Samelson on the invention of the push-pop stack.

After the Second World War, when his radar service at the Australian Air Force was interrupted, Hamblin studied mathematics, physics, and philosophy at the University of Melbourne and attained a doctorate in 1957 at the London School of Economics. From 1955 up to his death, he was a professor of philosophy at the University of New South Wales. In the second half of the 1950s, he became active with the third computer available in Australia, a copy of the DEUCE computer by the English Electric company.

For the DEUCE, Hamblin sketched one of the first programming languages, GEORGE, which was based on Reverse Polish Notation, including the associated compiler (language translator), which translated programs formulated in GEORGE into the machine language of the computer. His work is considered the first with Reverse Polish Notation, and this is why he is sometimes called an inventor of this representation method. Whether or not he independently invented the notation and its usage, he showed the merit, service, and advantage of the Reverse Polish way of writing programs for the processing on programmable computers and algorithms to make it happen.

The second direct result of his work with the development of compilers was the concept of the push-pop stack, which he developed independently of Friedrich Ludwig Bauer and Klaus Samelson, and for which in 1957 he was granted a patent for the use of a push-pop stack for translation by programming languages. In the same year, 1957, Hamblin presented his stack concept at the first Australian Computer Conference. His work had an impact on the development of stack-based computers, their machine instructions, their arguments on a stack, and reference addresses.

Into the 1960s, he again increasingly turned to philosophical questions. He wrote an influential introductory book on formal logic that is today a standard work on fallacies. It dedicated itself to the treatment of false conclusions by traditional logic, brought in formal dialectic, and developed it further. As such, Hamblin is considered one of the founders of modern informal logic.

He contributed to the development of modern temporal logic in two ways. In its very early period he corresponded with Arthur Prior between 1958 and 1965; this collaboration culminated with the so-called Hamblin implications. Later, in 1972, he independently rediscovered a form of duration calculus (interval logic), without being aware of the 1947 work of A. G. Walker on this topic, who was not interested in the tense aspect. His duration calculus is very similar to that later developed by James Allen and Patrick J. Hayes in the mid-1980s.

In addition to ancient Greek, Hamblin was familiar with several Asian and Pacific languages. A classical music lover who played the piano, he was setting words of Wittgenstein to music while hospitalized with an affliction that proved fatal.

Among his influential articles are: "Translation to and from Polish Notation," The Computer Journal 5/3, October 1962, pp. 210–213; "An Addressless Coding Scheme based on Mathematical Notation," W.R.E. Conference on Computing, Proceedings, Salisbury: Weapons Research Establishment, 1957; "GEORGE, an Addressless Coding Scheme for DEUCE," Australian National Committee on Computation and Automatic Control, Summarized Proceedings of First Conference, paper C6.1, 1960; and "Computer Languages," The Australian Journal of Science 20, pp. 135–139, reprinted in The Australian Computer Journal 17/4, pp. 195–198 (November 1985).