The first programming language to allow functions to be recursively defined was McCarthy’s LISP in 1959. Its introduction was not controversial: nobody but John McCarthy had any say in what the language was going to be. In addition to his work on LISP, McCarthy was on the committee finalizing the Algol language in 1959 and 1960. In spite of the fact that a majority was opposed to it, the definition of Algol 60 ended up allowing recursively defined procedures. In  I gave an acount of how this happened.
Why was recursion such a big deal? For us this is hard to understand: for decades the programming language C, not exactly a paradigm of avant-garde, has allowed recursion. Still, remnants of unease remain. Still, in some introductory courses, recursion plays the role of a pons asinorum. Have instructors been traumatized by a sarcastic teacher finding, oh horrors, a circular definition in their high-school essay? In this essay I’m going to explore recursion by contrasting it to its opposite, iteration.