1.7 LISP as Maxwell’s Equations of Software

As fate would have it, I stumbled upon this interview with Alan Kay, where he shares a revelation he had when reading John McCarthy’s LISP-1.5 manual:

that was the big revelation to me … when I finally understood that the half page of code on the bottom of page 13 of the Lisp 1.5 manual was Lisp in itself. These were “Maxwell’s Equations of Software!” This is the whole world of programming in a few lines that I can put my hand over.

Our starting point is hex0, a 500 byte hex assembler and we need to somehow close the gap to building the bootstrap binary seed, esp. GNU Gcc and the GNU C Library. What better way to do that than by leveraging the powers of LISP?

GNU Mes is a Scheme¹² interpreter that will be indirectly bootstrapped from hex0 and that wields the magical powers of LISP to close the bootstrap gap, asserting we can enjoy software Freedom 1.

• Auditable Elegance

(define (apply fn x a)
  (cond
   ((atom fn)
    (cond
     ((eq fn CAR)  (caar x))
     ((eq fn CDR)  (cdar x))
     ((eq fn CONS) (cons (car x) (cadr x)))
     ((eq fn ATOM) (atom (car x)))
     ((eq fn EQ)   (eq (car x) (cadr x)))
     (#t           (apply (eval fn a) x a))))
   ((eq (car fn) LAMBDA)
                   (eval (caddr fn) (pairlis (cadr fn) x a)))
   ((eq (car fn) LABEL)
                   (apply (caddr fn) x
                          (cons (cons (cadr fn) (caddr fn)) a)))))

(define (eval e a)
  (cond
   ((atom e) (cdr (assoc e a)))
   ((atom (car e))
    (cond ((eq (car e) QUOTE) (cadr e))
          ((eq (car e) COND)  (evcon (cdr e) a))
          (#t                 (apply (car e) (evlis (cdr e) a) a))))
   (#t       (apply (car e) (evlis (cdr e) a) a))))