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My attempt to implement an interpreter for the original LISP.
x = atom
(x . y) = s-expression
(atom x) -> t IF x is an atom
(atom (x . x)) -> nil
(eq x y) -> t if x and y are both atomic and refer to the same symbol
(eq x x) => t
(eq x y) => nil
(eq x (x . y)) => undefined
(car x) -> defined only if x is not atomic
(car (e1 . e2)) => e1
(car (x . a)) => x
(car ((x . a) . y)) => (x . a)
(cdr x) ->
(cdr (e1 . e2)) => e2
(cons x y) -> for any x y
(cons x x) -> (x . x)
(cons e1 e2) -> (e1 . e2)
(cond (e1 s1) (e2 s2) (e3 s3)) ->
returns the first sN for which eN evaluates to t
(ff x) ->
((atom x) x)
(t (ff (car x))))
(defun (subst x y z)
"the result of substituting the sexpr x for all
occurrences of the atomic symbol y in the sexpr z"
((atom z) (cond
((eq z y) x)
(t z)))
(t (cons (subst x y (car z))
(subst x y (cdr z))))))
(defun (and x y)
(x y)
(t nil)))
(defun (or x y)
(x t)
(t y)))
(defun (not x)
(x nil)
(t t)))
(defun (weirdo p q)
(p q)
(t t)))
(defun (equal x y)
(or (and (atom x) (atom y) (eq x y))
(and (not (atom x)) (not (atom y))
(equal (car x) (car y))
(equal (cdr x) (cdr y)))))
(defun (null x)
(and (atom x) (eq x nil)))
(defun (cadr x)
(car (cdr x)))
(defun (caddr x)
(car (cdr (cdr x))))
;; etc.
(defun (list a b c)
(cons a (cons b (cons c nil))))
(defun (append x y)
((null x) y)
(t (cons (car x)
(append (cdr x) y)))))
(defun (apply f args)
(eval (cons f (appq args)) nil))
(defun (appq m)
((null m) nil)
(t (cons (list 'quote (car m))
(appq (cdr m))))))
(defun (eval e a)
((atom e) (assoc e a))
((atom (car e))
((eq (car e) 'quote)
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