--- Paul Hudak: Sierpinski Triangle
--- See: The Haskell School of Expression, Chapter 3

import SOEGraphics

spaceClose :: Window -> IO ()
spaceClose w =
    do k <- getKey w
       if k == ' ' then closeWindow w
	  else spaceClose w

fillTri :: Window -> Int -> Int -> Int -> IO ()
fillTri w x y size
    = drawInWindow w (withColor Blue (polygon [(x,y), (x+size, y), (x,y-size), (x,y)]))

minSize :: Int
minSize = 18

sierpinskiTri :: Window -> Int -> Int -> Int -> IO ()
sierpinskiTri w x y size 
	      = if size <= minSize
		then fillTri w x y size
		else 
		  let size2 = size `div` 2
		  in do sierpinskiTri w x y size2
			sierpinskiTri w x (y-size2) size2
			sierpinskiTri w (x+size2) y size2

main0 
  = runGraphics (
      do w <- openWindow "Sierpinski Triangle" (350, 350)
         sierpinskiTri w 50 300 256
	 spaceClose w)