This article has many misstatements in its first half. > John McCarthy wrote 6 easy things in machine code, then combined them to make a programming language.

This article has many misstatements in its first half. > John McCarthy wrote 6 easy things in machine code, then combined them to make a programming language. John McCarthy didn't implement Lisp in machine code. Steve Russell did. Implementing Lisp properly in machine code is not easy; you have to write a garbage collector. To do that in the early 60s, you had to first invent garbage collection. Lisp was and is brilliant, but not as easily bootstrappable as this makes it out to be. > It's not obvious that these six things are computationally complete (AKA Turing Complete). `lambda` and function application alone are Turing-complete, as McCarthy would have known. The credit here belongs with Turing and Church, not McCarthy. `atom`, `cons`, `car` and all the rest are just icing on the cake of the lambda calculus when it comes to computability. > All other meaning can be defined in terms of them. Yes, and you can build everything on top of the SK combinator calculus if you like, but that doesn't make it a good idea. Lisp is surprisingly practical given how few core constructs it has, but real Lisp implementations have always added more primitives (eg. numbers and addition) for reasons of practicality. > The language was defined in terms of itself as an interpreter. This is a proof by construction that the language is computationally complete. No, it isn't. To prove Turing-completeness you need to show that you are as powerful as Turing machines. To do this it suffices to show that you can interpret a language already known to be Turing-complete. Showing you can interpret yourself does not suffice. It's easy to define a language which can do nothing useful except interpret itself, for example. (See also wyager's comment.) > Well, Lisp is defined as an interpreter in terms of itself from the get-go, just like a Universal Turing Machine. No. Defining a language only in itself is nonsense, for exactly the reason given above: it means nothing yet! It's like writing in a dictionary: qyzzyghlm, v. intr. To qyzzyghlm. It explains nothing unless you already understand it! > Lisp is a universal language because it can interpret its own code. While you can certainly write a JavaScript interpreter in JavaScript, none of the work is done for you. Almost none of the work is done for you in Lisp either. The core of Lisp is just a relatively easy language to implement, while Javascript is a difficult one. Lisp is easy to implement because it has simple syntax (s-expressions) and few core constructs. The only thing that is special about implementing Lisp in Lisp is that Lisp uses s-expressions as its core data structure, so you don't have to invent an AST representation. The article, to its credit, explores this idea later.