#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 radius)
  (* 2 pi radius))



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



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



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



(define (sum-of-squares 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 student)
  (apply average (rest student)))




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



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


(define (love-animals animal1 animal2)
  (string-append "I love baby " animal1 " and " animal2 "."))



(define (love-favorite fav)
  (lambda (animal2)
    (love-animals fav animal2)))



;; -----------------------------------------------------------------
;; 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 . grades)
  (/ (apply + grades)
     (length grades)))

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