SICP_3.26

(define false #f)
(define true #t)

(define (make-table)
  (let ((local-table '()))

    (define (make-tree key value left-branch right-branch)
      (list (cons key value) left-branch right-branch))

    (define (record-key tree)
      (caar tree))
    
    (define (record-value)
      (cdar tree))
    
    (define (left-sub tree)
      (cadr tree))
    
    (define (right-sub tree)
      (caddr tree))
    
    (define (record tree)
      (car tree))

    (define (lookup key)
      (define (lookup-helper tree)
        (if (null? tree)
            false
            (if (= (record-key tree) key)
                (record-value tree)
                (if (< (record-key tree) key)
                    (lookup-helper (left-sub tree))
                    (lookup-helper (right-sub tree))))))
      (lookup-helper local-table))

    (define (insert! key value)
      (define (insert-helper! tree)
        (if (null? tree)
            (set! tree (make-tree key value '() '()))
            (if (= (record-key tree) key)
                (set-cdr! (record tree) value)
                (if (< (record-key tree) key)
                    (insert-helper! (left-sub tree))
                    (insert-helper! (right-sub tree))))))
      (insert-helper! local-table)
      'ok)

    (define (print-table)
      (display local-table)
      (newline))

    (define (dispatch m)
      (cond ((eq? m 'print-table) print-table)
            ((eq? m 'insert!) insert!)
            ((eq? m 'lookup) lookup)
            (else (error "Unknow operation --TABLE" m))))

    dispatch))

(define t1 (make-table))
((t1 'print-table))
((t1 'lookup) 4)
((t1 'insert!) 4 'lan)
((t1 'insert!) 5 'tian)
((t1 'print-table))

insert!   部分有问题明明set！ 了 local-table 却没有什么效果，可能是我对环境模型的理解不够导致的。           参考