make-table.rkt

(require srfi/1)

(define (make-table)
  (let loop ((local-table `(*table*)))
    (letrec ((lookup 
              (lambda (key-1 key-2)
                (let ((subtable (assoc key-1 (cdr local-table))))
                  (when subtable
                    (let ((record (assoc key-2 (cdr subtable))))
                      (when record
                        (cdr record)))))))
             (insert 
              (lambda (key-1 key-2 value)
                (let ((head (car local-table))
                      (subtable (assoc key-1 (cdr local-table))))
                  (if subtable
                      (let ((record (assoc key-2 (cdr subtable))))
                        (loop (cons head
                                    (alist-cons 
                                     key-1
                                     (alist-cons key-2 value
                                                 (if record
                                                     (alist-delete 
                                                      key-2
                                                      (cdr subtable))
                                                     (cdr subtable)))
                                     (alist-delete key-1 (cdr local-table))))))
                      (loop (cons head (cons `(,key-1 ,(cons key-2 value)) 
                                             (cdr local-table))))))))
             (dispatch
              (lambda (m)
                (case m
                  ((lookup-proc) lookup)
                  ((insert-proc) insert)
                  (else (error "Unknown operation -- TABLE" m))))))
      dispatch)))