FLOLAC'18 prerequisite p2

histogram.hs

stat :: [Int] -> [Int]
stat []     = replicate 10 0
stat (x:xs) = (take x stats) ++ [stats !! x + 1] ++ tail (drop x stats)
    where stats = stat xs

plot :: [Int] -> [String]
plot ys
    | all (== 0) ys = []
    | otherwise     = row : plot ys'
    where row = map (\y -> if y == 0 then ' ' else '*') ys
          ys' = map (\y -> max 0 $ y - 1) ys

histogram :: [Int] -> String
histogram xs = unlines $ reverse $ "0123456789" : "==========" : plot (stat xs)

{-
ghci> putStr $ histogram [1,4,5,4,6,6,3,4,2,4,9]
    *
    *
    * *
 ******  *
==========
0123456789
-}