A Mandelbrot Set visualizer in Haskell

Mandelbrot.hs

module Mandelbrot where

import Graphics.UI.SDL as SDL

import System.Exit

resolution = 30

drawSlowly = True

imageWidth  = 400
imageHeight = 400

minRe = -2.0
maxRe = 1.0
minIm = -1.2
maxIm = minIm + (maxRe - minRe) * (imageHeight / imageWidth)

reFactor = (maxRe-minRe)/(imageWidth-1)
imFactor = (maxIm-minIm)/(imageHeight-1)

imageArray   = [ (x,y) | x <- [0.. floor imageWidth - 1], y <- [0.. floor imageHeight - 1] ]

inSet :: (Fractional a, Ord a) => (a,a) -> Bool
inSet (x,y) = if resolution == (length $ take resolution $ takeWhile (\ (x,y) -> x^2 + y^2 < 4) $ iterate (\ (zRe, zIm) -> (zRe^2 - zIm^2 + x , 2 * zRe * zIm + y ) ) (x,y) )then True else False

drawSet :: SDL.Surface -> IO ()
drawSet screen = do 
  putStrLn "Building Image.. please wait! "
  black <- SDL.mapRGB (SDL.surfaceGetPixelFormat screen) 0 0 0
  mapM_ (\ (x,y) -> if inSet (minRe + fromIntegral x * reFactor, maxIm - fromIntegral y * imFactor ) then (fillRect screen (Just $ SDL.Rect x y 1 1 ) black) >> (if drawSlowly then SDL.flip screen else return ()) else return () ) imageArray
  SDL.flip screen
  putStrLn "Done! "

initSDL :: IO Surface
initSDL = do
  SDL.init [SDL.InitEverything]
  SDL.setVideoMode (floor imageWidth) (floor imageHeight) 32 []
  SDL.setCaption "Mandelbrot" "Mandelbrot"
  screen <- getVideoSurface
  white <- SDL.mapRGB (SDL.surfaceGetPixelFormat screen) 255 255 255
  fillRect screen Nothing white >> SDL.flip screen
  return screen

exitHandler :: IO ()
exitHandler = do
  e <- waitEvent
  case e of
    Quit -> SDL.quit
    otherwise -> exitHandler

main :: IO ()
main = do
  s <- initSDL
  drawSet s
  exitHandler