simple lolcat powered by haskell

lolcat.hs

import Data.Word

freq = 0.3
spread = 8.0

unbase :: Integral int => int -> Word8 -> Word8 -> Word8 -> int
unbase base r g b = (fi r*base+fi g)*base+fi b
    where fi = fromIntegral

-- | Approximate a 24-bit Rgb colour with a colour in the xterm256 6x6x6 colour cube, returning its index.
rgb24bit_to_xterm256 :: (Integral t) => Word8 -> Word8 -> Word8 -> t
rgb24bit_to_xterm256 r g b = let f = (`div` 43)
                          in 16 + unbase 6 (f r) (f g) (f b)

lolcat _ [] = ""

lolcat (color, lineColor, ansi) ('\n':xs) =
    "\n" ++ lolcat (color', color', ansi) xs
    where color' = lineColor + 1

lolcat (color, lineColor, ansi) ('\ESC':xs) =
    lolcat (color, lineColor, True) xs

lolcat (color, lineColor, True) ('m':xs) =
    lolcat (color, lineColor, False) xs

lolcat (color, lineColor, True) (x:xs) =
    lolcat (color, lineColor, True) xs

lolcat (color, lineColor, False) (x:xs) =
    "\ESC[38;5;" ++ colored ++ "m" ++ [x] ++ "\ESC[0m" ++ lolcat (color + 1 / spread, lineColor, False) xs
    where red   = round (sin (freq * color) * 127) + 128
          green = round (sin (freq * color + 2 * pi / 3) * 127) + 128
          blue  = round (sin (freq * color + 4 * pi / 3) * 127) + 128
          colored = show $ rgb24bit_to_xterm256 red green blue

main = interact $ lolcat (0, 0, False)