self-lambda

gistfile1.lisp

#|
usage:
(funcall (self-lambda (n) (if (> n 0) 
                            (self (- n 1))
                            n))
          5)
|#

(defmacro self-lambda (param-lst &rest body)
  (let ((fn (gensym)))
    (labels ((replace-self (lst) ;replace "self" to "funcall fn fn"
                (cond
                  ((null lst) nil)
                  ((not (listp lst)) lst)
                  ((eql (car lst) 'self)
                      (append `(funcall ,fn ,fn) (replace-self (cdr lst))))
                  ((listp (car lst)) 
                      (cons (replace-self (car lst)) (replace-self (cdr lst))))
                  (t
                      (cons (car lst) (replace-self (cdr lst)))))))
      (let ((new-param '()) (param-length (list-length param-lst)))
        (do ((i 0 (+ i 1)))
          ((= i param-length) nil)
          (setf new-param (cons (gensym) new-param)))
        `(lambda (,@new-param)
           (labels ((lmbd (,fn ,@param-lst) 
                         ,@(mapcar #'replace-self body))) 
             (funcall #'lmbd #'lmbd ,@new-param)))))))