Chrisopher Strachey was the most significant contributor to the design and implementation of the programming language CPL.
At the time there was little understanding of the complexities of computer language design and how type systems could cope with lists and the kinds of structures needed to represent, for instance, parse trees. The CPL project cannot be regarded as being successful since it did not result in a usable CPL compiler. The reasons being that the language became too large and complicated, there were insufficient people to implement the compiler and, in the middle of the three year project, all work had to be transferred from Edsac 2 to Titan, a newly designed version of the Ferranti Atlas computer which as yet had no operating system. Even so, we can be proud of the work that went into CPL and its influence on the design of many later languages.