(load-quietly-from-lib "ch3.ss") ; for list-of-zeros

; - Program 5.14, pg. 151 -

(define the-zero-poly '(0))

(define degree 
  (lambda (poly)
    (sub1 (length poly))))

(define leading-coef
  (lambda (poly)
    (car poly)))

(define rest-of-poly
  (lambda (poly)
    (cond
      ((zero? (degree poly)) the-zero-poly)
      ((zero? (leading-coef (cdr poly)))
       (rest-of-poly (cdr poly)))
      (else (cdr poly)))))

(define poly-cons
  (lambda (deg coef poly)
    (let ((deg-p (degree poly)))
      (cond
        ((and (zero? deg) (equal? poly the-zero-poly)) (list coef))
        ((< deg-p deg)
         (if (zero? coef)
             poly
             (cons coef 
                (append (list-of-zeros (sub1 (- deg deg-p))) 
                        poly))))
        (else (error "poly-cons: Degree too high in" poly))))))

; - End Program -