Thimbles & Care

This morning comes the news that John McCarthy, creator of Lisp, has died.

I always thought the story of how he wrote the first Lisp interpreter was interesting. McCarthy and his students had developed Lisp notation, but they heard how much effort went into the Fortran compiler and didn’t think they had the resources for that, so when they actually wanted to run a program they translated it to machine code by hand. Then McCarthy wrote a paper showing that Lisp was Turing-complete, and in the process he wrote an eval function that could interpret an arbitrary Lisp expression. When one of his grad students read the paper, he realized that once they translated that function to machine code they would have an interpreter that could run any Lisp program, and they wouldn’t have to translate by hand any more.