(define (vertical-line pt length)
  (lambda (t) (make-point (x-of pt)
                          (+ (* t length)
                             (y-of pt)))))
(define (horizontal-line pt length)
  (lambda (t) (make-point (+ (* t length) (x-of pt))
                          (y-of pt))))
(define (unit-circle-half pt)
  (lambda (t) (make-point (+ (x-of pt) (* 0.15 (sin (* 2pi (+ 0.25 (* 0.5 t))))))
                          (+ (y-of pt) (* 0.15 (cos (* 2pi (+ 0.25 (* 0.5 t)))))))))


(define J
  (lambda (t)
    (cond ( (< t (/ 1 3)) ((horizontal-line (make-point 0.2 0.8) 0.6) (* 3 t)))
          ( (< t (/ 2 3)) ((vertical-line (make-point 0.5 0.3) 0.5) (-  (* 3 t) 1)))
          (else ((unit-circle-half (make-point 0.35 0.3)) (- (* 3 t) 2))))))