practice for FLOLAC

histogram.hs

toRecord :: (Int -> Int) -> Int -> (Int -> Int)
toRecord r x y | x == y = (r x) + 1
               | otherwise = r y

histogram :: [Int] -> String
histogram xs = unlines (f record max) ++ "==========\n0123456789\n"
    where count = foldl toRecord (const 0) xs
          record = map count [0..9]
          max = maximum record

f :: [Int] -> Int -> [String]
f _ 0 = []
f record most = map (\x -> if x < most then ' ' else '*') record : (f record (most-1))