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

(define (shikoku? x)
        (or (eq? x 'kagawa) (eq? x 'tokushima)
            (eq? x 'ehime)  (eq? x 'kochi)))

(define (accute? x)          ; 鋭角か?
        (and (>= x 0) (< x 90)))

(define (hen_na_square x)
        (set! x (* x x)) 
        x)


(define (bar y) (set! x (+ x y)))

(define (2-ji-houtei-shiki a b c)
        (let ((D (- (* b b) (* 4 a c))))
         (if (> D 0)
             (let ((sqrt-d (sqrt D)))
              (list (/ (+ (- b) sqrt-d) (* 2 a))
                    (/ (- (- b) sqrt-d) (* 2 a))))
             '())))


(define (baz x) (let* ((y (list x x))
                       (z (list y y)))
                 (list z z)))


(define (qux x) (set! x (* x x)) x)

(define (fact n)
        (if (= n 1) 1 (* n (fact (- n 1)))))


(define (fern g d x y r t)
; (x, y) --- 付け根の位置, r --- 長さ, t --- 角度  
  (if (= d 0)
      #t
    (let ((dx (* r (cos t)))
          (dy (* r (sin t))))
      (graphics-draw-line g x y (+ x dx) (+ y dy))
      (fern g (- d 1)          ; 幹
            (+ x (* 1.0  dx)) (+ y (*  1.0 dy)) (* r 0.7)  (+ t 0.17))
      (fern g (- d 1)          ; 右の枝
            (+ x (* 0.45 dx)) (+ y (* 0.45 dy)) (* r 0.45) (- t 1.40))
      (fern g (- d 1)          ; 左の枝
            (+ x (* 0.55 dx)) (+ y (* 0.55 dy)) (* r 0.40) (+ t 1.30)))))


;(define (fact n)
;        (do ((i 1 (+ i 1))
;             (r 1 (* r i)))     
;            ((> i n) r)
;            #t)) ; ここでは何もする必要がないので適当な式を書いておく。

(define PI 3.1416)
(define PI_2 (/ PI 2))
(define (draw-ngon g x y r t n)
        (do ((delta (/ (* 2 PI) n) delta)  ; 最後の deltaは省略可
             (i 0 (+ i 1)))
            ((>= i n) #t)    ; #tに特別な意味はない
            (let ((theta1 (+ (* delta i) t))
                  (theta2 (+ (* delta (+ i 1)) t))) 
              (graphics-draw-line g (* r (cos theta1)) (* r (sin theta1))
                                    (* r (cos theta2)) (* r (sin theta2))))))   

(define (hanoi n a b c)   ; n個の円盤を棒 aから棒 bに  
   (if (= n 1) 
       (move_disk_from_to 1 a b)  
       (begin
          \myspace{(hanoi (- n 1) a c b)}
          (move_disk_from_to n a b)  
          \myspace{(hanoi (- n 1) c b a )}
       )))


(define (move_disk_from_to d a b)
        (display "Move disk ")
        (display d)
        (display " from ")
        (display a)
        (display " to ")
        (display b)
        (newline))