Christopher Strachey: A Personal Recollection

Abstract

At the beginning of the 1950s Christopher Strachey was teaching mathematics at Harrow, a traditional English public school. At the age of fourteen I, along with some 20 other boys in the Classical Lower Fifth, was fortunate enough to be among his pupils. We had already chosen the focus of our academic work – to specialise in the language, literature and history of the ancient Greeks and Romans. For us the study of mathematics was an option, unconstrained by any examination syllabus or any need to adhere to a predefined curriculum. Christopher treated it as a freeranging exploration of mathematical ideas. He discussed Klein bottles and Moebius strips. He introduced us to some of Cantor’s ideas about countable and uncountable infinities, to group theory and simple applications of matrix algebra. We explored binary notation and other number representations; we analysed the game of nim, and we went to see Nimrod, the Ferranti nim-playing computer exhibited at the Festival of Britain in 1951. Christopher also introduced us to computer programming. At the time, he was writing experimental programs for the computer at Manchester university: neat columns of numeric machine-code instructions, the jumps carefully annotated with pencilled arrows leading to their targets. He encouraged us to write programs of our own, expressed as flowcharts. For the operation and condition boxes he devised a little language with variable names, assigment, simple integer expressions of one add or subtract operator, and tests for equality with zero. I remember my pride in my programs for integer multiplication and division, but I can not recollect any scheme for converting them to subroutines for general use. Christopher’s own programs were of a different calibre. He wrote a program to play draughts (or checkers). The program was punched into 5-hole paper tape in London; loaded into the machine in Manchester, it ran perfectly first time. But