firstTo40.hs

import Data.Char
import Data.List
digitSum :: Int -> Int
digitSum = sum . map digitToInt . show
-- find :: (a -> Bool) -> [a] -> Maybe a
firstTo40 :: Maybe Int
firstTo40 = find (\x -> digitSum x == 40) [1..]
firstTo :: Int -> Maybe Int
firstTo n = find (\x -> digitSum x == n) [1..]

main = do
    print $ digitToInt '2'
    print $ digitToInt 'F'
    print $ digitSum 4444
    print $ firstTo40 -- 49999
    print $ firstTo 40 -- 49999
    print $ firstTo 27 -- 49999