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Comment by mroll | Hacker News Reader

Nice article. Check out Paul graham's The Roots of Lisp for a similar exploration in which he shows how to build the metacircular interpreter.

> John McCarthy wrote 6 easy things in machine code

It was actually Steve Russel, McCarthy's grad student, who had the idea of writing McCarthy's eval function in machine code.

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> It was actually Steve Russel

I seem to recall reading that McCarthy was actually surprised to discover that Lisp _could_ be run by a real computer; he intended it to be a completely theoretical tool.

I have also heard that, but only from secondary sources. Here is a clip of Russell talking about the time he wrote the first lisp interpreter. He doesn't mention McCarthy being surprised, but he seems to imply that he, Russell, was quicker to grasp the idea of translating the functions McCarthy had been writing to machine code.

http://www.computerhistory.org/pdp-1/1020b307d766e0019de2b4a...

No, that's definitely wrong. Initially they compiled LISP code into assembly by hand (when LISP still looked a lot like fortran) and the plan was to write a compiler in assembly to automate that. Instead, McCarthy came up with a way to express LISP code (aka M-expressions) as data (aka S-expressions) to give a definition the LISP semantics in LISP itself. Steve Russell then hand compiled this definition, and lo, they had a working interpreter of S-expressions. M-expressions were never implemented and the compiler was written in LISP instead of assembly.

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