There are a bunch of confusions to the relationship of LISP, the LISP system and the LISP paper of 1960.<p>The "original paper on Lisp" is from 1960: <a href="http://www-formal.stanford.edu/jmc/recursive.html" rel="nofollow">http://www-formal.stanford.edu/jmc/recursive.html</a><p>A bunch of papers about the design and development of LISP and the LISP system had been published earlier. Those show the various stages of the project to define and implement the new language. See for example: <a href="https://www.softwarepreservation.org/projects/LISP/lisp15_family#LISP_I_and_LISP_1.5_for_IBM_704,_709,_7090_" rel="nofollow">https://www.softwarepreservation.org/projects/LISP/lisp15_fa...</a><p>By that time of publishing the paper on LISP, an actual "LISP system", the practical implementation of LISP existed. To quote from above's paper: "A programming system called LISP (for LISt Processor) has been developed for the IBM 704 computer by the Artificial Intelligence group at M.I.T.". "has been" and not "will be".<p>The manual of this first LISP system, called Lisp I, is here in a version of March 1960: <a href="http://bitsavers.org/pdf/mit/rle_lisp/LISP_I_Programmers_Manual_Mar60.pdf" rel="nofollow">http://bitsavers.org/pdf/mit/rle_lisp/LISP_I_Programmers_Man...</a><p>The "LISP Programming System" is described in Chapter 4. It had functions, numbers (floats) and a machine code compiler. Chapter 5 describes input from punched cards, function tracing and a interface to an online printer/keyboard. Chapter 6.3 describes the garbage collector. Chapter 9 describes the available (ninety) functions, including eval, map, maplist, print, read, compile, matrixmultiply and a bunch of others.<p>So it is fair to say that the development of a theoretical foundation and the LISP system itself was not just "somewhat interleaved", but were basically completely interleaved, both together were done incrementally.<p>The process was not to 'first define theoretical foundations, then a language definition and then an implementation'. It was always all three combined, with a real practical LISP system on a real computer, developed incrementally at that time.