#lang racket

;; modify type-tag, contents, and attach-tag so that primitive numbers need not
;; be tagged.

(define (type-tag datum)
  (cond 
    [(pair? datum) (car datum)]
    [(number? datum) 'scheme-number]
    [else 
     (error "Bad tagged datum -- TYPE-TAG" datum)]))

(define (contents datum)
  (cond 
    [(pair? datum) (cdr datum)]
    [(number? datum) datum]
    [else
     (error "Bad tagged datum -- CONTENTS" datum)]))

(define (attach-tag type-tag contents)
  (if (number? contents)
      contents
      (cons type-tag contents)))