gistfile1.sls

(defun make-stat-env (params &optional env (position 1) num-env)
  (unless num-env (setq num-env (+ (or (second (first env)) -1) 1)))
  (cond ((endp params)
         env)
        ((eq '&optional (car params))
         `((,(cadr params) ,num-env ,position)
           (,(intern (format nil "~a-P" (cadr params))) ,num-env ,(+ 1 position))
           . ,(make-stat-env (cddr params) env (+ 2 position) num-env)))
        ((eq '&rest (car params))
         (make-stat-env (cdr params) env position num-env))
        (t
         `((,(car params) ,num-env ,position)
            . ,(make-stat-env (cdr params) env (+ 1 position))))))

(make-stat-env '(a b &optional c))
=> ((A 0 1) (B 0 2) (&OPTIONAL 0 3) (C 0 4))