CSC151 2007S, Class 13: Recursion with Lists

Admin:
* HW6 returned (via email).  More grading on the near horizon.
* If there's a snow day on Tuesday, I may be bringing my children
  to class.
* Reading for tomorrow: Recursion with Natural Numbers.

Overview:
* Q&A.
* Labs.

; Proceeds and profits in the Spencer Grill

(define coffee-proceeds
  (lambda (small large)
    (+ (* small 175) (* large 290))))
(define coffee-profits
  (lambda (small large)
    (- (coffee-proceeds small large) 
       (coffee-costs small large))))
(define coffee-costs
  (lambda (small large)
    (* cost-per-ounce (+ (* small ounces-per-small) (* large 20)))))
(define cost-per-ounce 5)
(define ounces-per-small 12)
(define ounces-per-large 20)
(define profit-per-small
  (- cost-per-small (* cost-per-ounce ounces-per-small)))

; Procedures you should know
(string-ref str pos) - Extract the character at position pos from str
(char-ci=? ch1 ch2)