[Shootout-list] mandelbrot GHC

[Greg Buchholz]

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  Attached is a GHC version of the mandelbrot test in the sandbox.

Greg Buchholz


		
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Content-Type: text/x-haskell; name="fractal.hs"
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-- Fractal.hs mandlebrot example
-- dumps a *.ppm graphics file to stdout
-- compile:  ghc -O2 -o fractal fractal.hs
-- run: fractal 600 >mandel.pbm
-- by Greg Buchholz

import Complex
import System(getArgs)
import Char(chr)

main = do   [arg] <- getArgs
            let width = read arg
            let pts = points width width        
            putStr $ "P4\n" ++ arg ++ " " ++ arg ++ "\n"
            putStr $ concatMap (makePBM 0 0) (chunk width (fractal pts))
            
limit  = 2
iter   = 50+1 -- add one to compensate for the 'iterate' function

points width height = [(2*x/w - 1.5) :+ (2*y/h - 1) | y<-[0..h-1], x<-[0..w-1]]
                    where w = fromIntegral width
                          h = fromIntegral height

mandel c z = z * z + c

fractal pts = map (\f-> length (takeIter (iterate f (0:+0)))) (map mandel pts)
        where takeIter a = take iter (takeWhile (\x-> magnitude(x)<limit) a)
       
makePBM i acc []     = (chr (acc * 2^(8-i))) : []
makePBM i acc (x:xs) | i==8      = (chr acc) : makePBM 0 0 (x:xs)
                     | otherwise = makePBM (i+1) n xs
                                    where
                                      n = if x==iter then (acc*2+1) else (acc*2)

chunk width [] = []
chunk width c  = (fst split) : chunk width (snd split)
                 where split = splitAt width c
                    

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