Practice 2.89

the part same as the example in book

(define (the-empty-termlist) '())

(define (empty-termlist? term-list) (null? term-list))

the part have to modified

(define (adjoin-term term term-list)
  (let ((len (- (order term) (order (first-term term-list)))))
    (define (ajoin-zero-iter term-list times)
      (if (= 0 times)
          term-list
          (ajoin-iter (cons 0 term-list) (- times 1))))
    (cons (coeff term) (ajoin-zero-iter term-list len))))

(define (first-term term-list)
  (make-term (- (length term-list) 1) (car term-list)))

(define (rest-term term-list)
  (if (= 0 (cadr term-list))
      (rest-term (cdr term-list))
      (cdr term-list)))