Well, it has some element of truth. The S-expression notation we think of as “Lisp” originated as a contribution to recursive function theory rather than a practical programming language, even if earlier McCarthy was thinking of proceeding by adding IPL-V facilities to Fortran.

McCarthy wanted a list processing language. He added list processing functions (which then later appeared in Lisp) to Fortran. He and his team then went on to develop and implement a new language: Lisp. The implementation ALWAYS was based on lists and s-expressions.

The paper http://www-formal.stanford.edu/jmc/recursive.html was published, when Lisp was already implemented, to present some ideas to a different audience. But Lisp already existed by then as a running programming language.

First and foremost Lisp was a real programming language implemented on a real computer.

http://www.softwarepreservation.org/projects/LISP/lisp15_fam...

See also: History of Lisp, John McCarthy, http://jmc.stanford.edu/articles/lisp/lisp.pdf

"My desire for an algebraic list processing language for artificial intelligence work on the IBM 704 computer arose in the summer of 1956..."

"The implementation of LISP began in Fall 1958 ... These included programs to read and print list structure. I can’t now remember whether the decision to use parenthesized list notation as the external form of LISP data was made then or whether it had already been used in discussing the paper differentiation program."

"The M-notation also used brackets instead of parentheses to enclose the arguments of functions in order to reserve parentheses for list-structure constants. It was intended to compile from some approximation to the M-notation, but the M-notation was never fully defined, because representing LISP functions by LISP lists became the dominant programming language when the interpreter later became available."

"Anyway, I decided to write a paper describing LISP both as a programming language and as a formalism for doing recursive function theory. The paper was Recursive functions of symbolic ex- pressions and their computation by machine, part I (McCarthy 1960)."

An amusing coda to the M-notation story is that many extant examples of it closely resemble or are valid K/Q syntax.

Right, that's exactly what I mean. Thank you for a adding all these great references to primary sources! Has CBI or somebody done an oral history interview with Slug Russell yet covering this time period? He's not dead yet. There's still time.

Just that the s-expression notation did not originate as contribution to recursive function theory, but was actually originating from designing and implementing a programming language and system for list processing.

I think your reading of these sources differs from mine, then, but the important thing is that now anyone who is interested can peruse them at their leisure and make up their own mind.

Yes. Originally it was a thought experiment. Just like mathematicians can imagine an idea and use a notation without creating a compiler.

Sure not. McCarthy wanted to develop a list processing system for the IBM 704 in the mid 50s. He experimented with Fortran and added list processing primitives and then went on to design and implement a new language: Lisp

McCarthy early on proposed to write a compiler - actually this was one of the very very early papers:

J. McCarthy. Memo to P. M. Morse: A Proposal for a compiler. Memo CC-56, Computation Center, Massachusetts Institute of Technology, December 13, 1957, 19 pages.

http://www.softwarepreservation.org/projects/LISP/MIT/CC-56....