;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;             U. C. Berkeley            ;;
;;      EECS Computer Science Division   ;;
;;         CS3 Lecture 21 Answers        ;;
;;            (Input / Output)           ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; Formatting ... 
;; We'll use [ ] to highlight what the user types to (read), 
;; ==P to indicate what the computer PRINTS, and 
;; ==> to indicate the return value (as always)

;;;;;;;;;;
;; STRINGS
;;;;;;;;;;

"Go Bears"
;; ==> "Go Bears"

(string? "Go Bears")
;; ==> #t

(string-length "Go Bears")
;; ==> 8

;;;;;;;;;
;; OUTPUT
;;;;;;;;;

(display 'a-symbol)
;; ==P a-symbol
;; ==> 8

(write 'a-symbol)
;; ==P a-symbol
;; ==> 8

(display "a string")
;; ==P a string
;; ==> 8

(write "a string")
;; ==P "a string"
;; ==> 10

;;;;;;;;;;;
;; FOR-EACH
;;;;;;;;;;;

(for-each abs '(-1 2 -3.4 -5/6))
;; ==P 
;; ==> #[undefined]

(define (print-list-one-elt-per-line L)
  (for-each
    (lambda (elt)
      (display elt)
      (newline))
    L)
  'done)

(print-list-one-elt-per-line 
  '("Cal Bears" (we are) Number 1))
;; ==P Cal Bears
;; ==P (we are)
;; ==P number
;; ==P 1
;; ==> done

;;;;;;;;;;;;;;;
;; IF AND BEGIN
;;;;;;;;;;;;;;;

;; : (big-game-winner-prediction 'cal)
;; ==P Party on! You were right that
;; ==P Cal will win the Big Game!
;; ==> done!
;;
;; : (big-game-winner-prediction 'stanfurd)
;; ==P Bzzt! Thanks for trying...
;; ==P stanfurd will not win the Big Game, Cal will!
;; ==> done!
;;
;; : (big-game-winner-prediction 'eat-my-shorts)
;; ==P Bzzt! Thanks for trying...
;; ==P eat-my-shorts will not win the Big Game, Cal will!
;; ==> done!

;; Here is the repaired version, the old version didn't even
;; let us define the function!

(define (big-game-winner-prediction team)
  (if (equal? team 'cal)
      
      ;; They predicted Cal
      (begin  
       (display "Party on! You were right that")
       (newline)
       (display "Cal will win the Big Game!"))
      
      ;; They didn't predict Cal
      (begin  
       (display "Bzzt! Thanks for trying...")
       (newline)
       (display team)
       (display " will not win the Big Game, Cal will!")))
  (newline)
  'done!)

;;;;;;;
;; READ
;;;;;;;

(read)
;; [42]
;; ==> 42

(read)
;; [cs3]
;; ==> cs3

(read)
;; [cs3 is the best class]
;; ==> class

(read)
;; ["cs3 is the best class"]
;; ==> "cs3 is the best class"

(read)
;; [(cs3 is the best class)]
;; ==> (cs3 is the best class)

(read)
;; [(+ 1 1) (+ 150 150)]
;; (+ 150 150)

;;;;;;;;;;;;;;;;;;
;; GET-VALID-INPUT
;;;;;;;;;;;;;;;;;;

;; read until input is in valid-input
;; print intro message to user first - prompt

(define (get-valid-input valid-input message)
  (display message)
  (display " ")
  (let ((input (read)))
    (cond ((member input valid-input)
            input)
          (else (display "Bad value entered: ")
                (display input)
                (newline)
                (get-valid-input valid-input message)))))

: (get-valid-input '(yes yep sure uh-huh) "Is CS3 cool?")
;; ==P Is CS3 cool? [maybe]
;; ==P Bad value entered: maybe
;; ==P Is CS3 cool? [well, I don't know...]
;; ==P Bad value entered: know...
;; ==P Is CS3 cool? [yes it is]
;; ==P Bad value entered: is
;; ==P Is CS3 cool? [yes]
;; ==> yes