sicp-ex-4.7

  
  
  
 ;; let* expression 
 (define (let*? expr) (tagged-list? expr 'let*)) 
 (define (let*-body expr) (caddr expr)) 
 (define (let*-inits expr) (cadr expr)) 
 (define (let*->nested-lets expr) 
         (let ((inits (let*-inits expr)) 
                   (body (let*-body expr))) 
                 (define (make-lets exprs) 
                         (if (null? exprs) 
                                 body 
                                 (list 'let (list (car exprs)) (make-lets (cdr exprs))))) 
                 (make-lets inits)))