The roots of Lisp by Paul Graham

In this article, the author Paul Graham tells the history (“the roots”) of the programming language Lisp. John McCarthy has built Lisp in 1958 with only few simple operators and a notation for functions. The name Lisp is a mix of the words “List” and “Processing”. Full of mockery was made because of the use of many parentheses in the Lisp syntax, giving a funny acronym for LISP: "Lots of Irritating and Silly Parentheses". Because of its expressiveness and flexibility, Lisp had a lot of success in the artificial intelligence community.

For the author, there are 2 unavoidable models nowadays: The C and Lisp programming languages, which influence the most recent languages (Most of the time, they are composed of a C base with adding Lisps parts, like runtime typing and garbage collection).

Paul Graham also explains how John McCarthy obtained his new model of computation by creating functions (eval). Lisp is a language that does not distinguish between "expressions" and "instructions" as many programming languages do. Clojure programs are composed of expressions. First of all, an expression is a sequence of letters or a list separated by whitespace and enclosed by parentheses. (foo bar) is an example of an expression (which is a list of 2 elements). The first element of a list is called an operator (examples: quote, atom, eq, car, cdr, cons, cond); the others are called the arguments. There are 3 main characteristics in the Lisp syntax: a Lisp program is a list of expressions, an expression can be an atom or a list (recursion), and an atom is either a number, a name, a string of characters, an operator.

The question that we can ask to ourselves is “why McCarthy didn’t use an already known model of computation such as the Turing machine?” These programs were just not enough interesting for the Lisp creator, not very edifying for him to read.