Simplest implementation of Voronoi diagram on Clojure

voronoi.clj

(ns voronoi-clojure.core
  (:gen-class)
  (:import (java.io File)
           (javax.imageio ImageIO)
           (java.awt.image BufferedImage)
           (java.awt.geom Ellipse2D Ellipse2D$Double)
           (java.awt Color)))

(defn- distance [x1 x2 y1 y2]
  (Math/sqrt (+ (* (- x1 x2) (- x1 x2)) (* (- y1 y2) (- y1 y2)))))

(defn -main
  "I don't do a whole lot ... yet."
  [& args]
  (let [cells 20
        size  1000
        px    (take cells (repeatedly #(rand-int size)))
        py    (take cells (repeatedly #(rand-int size)))
        color (take cells (repeatedly #(rand-int 16777215)))
        img   (BufferedImage. size size BufferedImage/TYPE_INT_RGB)
        gr    (.createGraphics img)]

    (with-local-vars [n 0]
      (doseq [x (range size)
              y (range size)
              i (range cells)]
        (do (cond (< (distance (nth px i) x (nth py i) y)
                     (distance (nth px (var-get n)) x (nth py (var-get n)) y))
                  (var-set n i))
            (.setRGB img x y (int (nth color (var-get n)))))))

    (.setColor gr (Color/BLACK))
    (doseq [i (range cells)]
      (.fill gr (Ellipse2D$Double. (nth px i) (nth py i) 5 5))

    (ImageIO/write img "png" (File. "test.png")))))

voronoi.png