gistfile1.hs

import Control.Arrow ((***))
import Control.Monad (join)
import Data.List (genericLength, mapAccumL)
import System (getArgs)

main = putStrLn . spark . map read =<< getArgs

spark = mapNormalize ((ticks!!) . round . (* (genericLength ticks - 1)))

ticks = " ▁▂▃▅▆▇"

mapNormalize :: (Ord a, Fractional a, Num a) => (a -> b) -> [a] -> [b]
mapNormalize f xs =
  let ((min',max'), runNormalize) =
        mapAccumL (\accumMinMax x ->
                    ((min x *** max x) accumMinMax,
                    f $ (x - min')/(max' - min')))
                  (join (,) $ head xs) xs
  in runNormalize