;;; (lambda (x) (+ x))
;;; (lambda (x) ((: free +) (: 0 0)))

(define lexical
    (lambda (datum bindings)
      (cond [(symbol? datum) (look-up datum bindings 0)]
	    [(pair? datum)
	     (cond [(eq? (car datum) 'lambda)
		    (list 'lambda
			  (cadr datum) 
			  (lexical (caddr datum)
				   (cons (cadr datum) bindings)))]
		   [else (list (lexical (car datum) bindings)
			       (lexical (cadr datum) bindings))])]
	    [else 'notImplemented])))

(define look-up
  (lambda (datum bindings depth)
    (cond [(null? bindings) (list ': 'free datum)]
	  [(memq datum (car bindings)) (list ': depth (get-pos datum (car bindings)))]
	  [else (look-up datum (cdr bindings) (+ depth 1))])))

(define get-pos
  (lambda (datum list)
    (cond [(null? list) 'error]
	  [(eq? datum (car list)) 0]
	  [else (+ 1 (get-pos datum (cdr list)))])))