#lang racket

;; -----------------------------------------------------------------
;; Questions about comments
;; -----------------------------------------------------------------

; a single-line comment

;; a single-line comment

#| a multi-line comment

   (fifth '(a b c d e))
   (list-ref '(a b c d e) 3)
   (eq? 'x '(x))

   that ends on the next line
|#

;; -----------------------------------------------------------------

;;    (* 2 pi 1)     ; for a circle with radius = 1
;;    (* 2 pi 10)    ; for a circle with radius = 10
;;    (* 2 pi 14.1)  ; for a circle with radius = 14.1


;; def circumference(radius):
;;     return 2 * pi * radius


;; (lambda (radius)
;;   (* 2 pi radius))



(define circumference
  (lambda (radius)
    (* 2 pi radius)))



;; (define (circumference radius)
;;   (* 2 pi radius))



;; -----------------------------------------------------------------



(define square
  (lambda (x)
    (* x x)))



(define sum-of-squares
  (lambda (x y)
    (+ (square x) (square y))))



;; -----------------------------------------------------------------



(define list-of-students
  '((jerry  3.7 4.0 3.3 3.3 3.0 4.0)
    (elaine 4.0 3.7 3.7 3.0 3.3 3.7)
    (george 3.3 3.3 3.3 3.3 3.7 1.0)
    (cosmo  2.0 2.0 2.3 3.7 2.0 4.0)))


;; (average 3.7 4.0 3.3 3.3 3.0 4.0)


(define compute-gpa
  (lambda (student)
    (apply average (rest student))))




(define sum-of-squares*              ;; takes a list, not just two
  (lambda (list-of-numbers)
    (apply + (map square list-of-numbers))))



;; -----------------------------------------------------------------
;; This is a helper function I used in the compute-gpa example.
;; We will learn how to write procedures like average next time.
;; -----------------------------------------------------------------

(define average
  (lambda grades
    (/ (apply + grades)
       (length grades))))

;; -----------------------------------------------------------------