Prog challenge:

Write Ascii85 to binary converter in 10 lines of code.
Hard Mode: Using Python.
Hardcore Mode: in Esoteric language of your choice.

import Control.Arrow
import Char

ascii85ToAscii [] = []
ascii85ToAscii ascii85 =
   uncurry (++) $ reverse . take 4 . map (chr . (`mod` 256)) . iterate (`div` 256) .
      foldl ((+) . (*85)) 0 . map (subtract 33 . ord) *** ascii85ToAscii $ splitAt 5 ascii85