In Peter Norvig's epic tome Paradigms of Artifical Intelligence Programming in Chapter 7 - he describes a function interp
which is effectively a simple eval
function used when interpreting a bare-bones Scheme in a REPL.
(defun interp (x &optional env)
"Interpret (evaluate) the expression x in the environment env."
(cond
((symbolp x) (get-var x env))
((atom x) x)
((case (first x)
(QUOTE (second x))
(BEGIN (last1 (mapcar #'(lambda (y) (interp y env))
(rest x))))
(SET! (set-var! (second x) (interp (third x) env) env))
(IF (if (interp (second x) env)
(interp (third x) env)
(interp (fourth x) env)))
(LAMBDA (let ((parms (second x))
(code (maybe-add 'begin (rest2 x))))
#'(lambda (&rest args)
(interp code (extend-env parms args env)))))
(t ;; a procedure application
(apply (interp (first x) env)
(mapcar #'(lambda (v) (interp v env))
(rest x))))))))
Interestingly enough - the opening Chapter of Christian Queinnec's Lisp In Small Pieces has a very similar function, he calls it eval
.
;;; This is a naive evaluator for Scheme written in naive Scheme.
(define (evaluate e env)
(if (atom? e)
(cond ((symbol? e) (lookup e env))
((or (number? e) (string? e) (char? e)
(boolean? e) (vector? e) )
e )
(else (wrong "Cannot evaluate" e)) )
(case (car e)
((quote) (cadr e))
((if) (if (evaluate (cadr e) env)
(evaluate (caddr e) env)
(evaluate (cadddr e) env) ))
((begin) (eprogn (cdr e) env))
((set!) (update! (cadr e) env (evaluate (caddr e) env)))
((lambda) (make-function (cadr e) (cddr e) env))
(else (invoke (evaluate (car e) env)
(evlis (cdr e) env) )) ) ) )
My question is - where is the Clojure source is the equivalent eval
/interp
function? I assume it is in the reader code somewhere.