drawMandelbrot.pde

void setup(){
  size(500, 500);
  translate(250, 250);
  String lines[] = loadStrings("mandelbrot.csv");
  for(String line : lines){
    String tmp[] = line.split(",");
    float x = (float(tmp[0]));
    float y = (float(tmp[1]));
    int count = 0;
    if(!tmp[2].equals("NIL")){
      count = int(tmp[2]);
    }
    stroke(0, count * 255 / 12, count * 255 / 12);
    point(round(x * 100), round(y * 100));
  }
}

mandelbrot.lisp

(defparameter *width* 500)
(defparameter *height* 500)
(defparameter *reduction* 100.0)

(defun get-latice-points (width height reduction)
  (apply #'append (loop for x from (* -1 (/ width 2)) below (1+ (/ width 2))
                        collect (loop for y from (* -1 (/ height 2)) below (1+ (/ height 2))
                                 collect (complex (/ x reduction) (/ y reduction))))))

(defun calc-mandelbrot (c)
  (labels ((f (z c n)
    (cond ((= n 27) `(,c nil))
          ((< 2 (abs z)) `(,c ,n))
          (t (f (+ c (expt z 2)) c (1+ n))))))
    (f 0 c 0)))

(defun get-mandelbrot ()
  (mapcar #'calc-mandelbrot (get-latice-points  *width* *height* *reduction*)))

(defun to-csv (coordinates-count)
  (let ((coordinates (car coordinates-count))
        (recursion-count (cadr coordinates-count)))
    (concatenate 'string 
                 (write-to-string  (realpart coordinates) ) "\," 
                 (write-to-string  (imagpart coordinates) ) "\," 
                 (write-to-string recursion-count))))

(defun to-csv-file (calculated-latice-points)
  (with-open-file (*standard-output* "mandelbrot.csv"
                                     :direction :output
                                     :if-exists :supersede)
    (mapcan (lambda (s)
              (format t (concatenate 'string s "~%")))
            (mapcar #'to-csv calculated-latice-points))))