; Draws the famous curve of Koch.
; Alejandro Luque Estepa, 1999

;First of all, we load the LispGraph package...
(import "zlisp.LispGraph")

(defun intercala (l p)
 (cond ((nullp (cdr l)) (append l p))
          (t (append (cons (car l) p) (intercala (cdr l) p)))
 )
)
(defun nintercala (l p n)
 (cond ((equal n 1) (intercala l p))
          (t (intercala (nintercala l p (sub1 n)) p ))
 )
)
(defun mtortuga (s a)
 (prog nil (right a) (forward s))
)
(defun camino (s p)
 (applytoall '(lambda (x) (mtortuga s x)) p)
)
; The old-known curve of Koch
(defun koch (s n)
   (camino s (nintercala '(0 120 120) '(-60 120 -60) n))
)
; A square variant
(defun square_koch (s n)
   (camino s (nintercala '(0 90 90 90) '(-90 90 90 -90) n))
)
(if (not (equal 0.1 1))
    (defun koch_sample nil
        (prog nil
            (cls 0.0 0.0 0.5)
            (color 1.0 1.0 0.0)
            (turtle 120 65 0)
            (pendown)
            (koch 3 4)
        )
    )
    (defun koch_sample nil
        (prog nil
            (cls 0,0 0,0 0,5)
            (color 1,0 1,0 0,0)
            (turtle 120 65 0)
            (pendown)
            (koch 3 4)
        )
    )

)

(msg "Usage: (koch s n) draws a Koch's curve of order n with segments of length s" t)
(msg "To view an example write (koch_sample) and evaluate while in graphics mode" t)