import Data.Char (digitToInt, isDigit)

sumDigitsRecur :: String -> Int
sumDigitsRecur [] = 0
sumDigitsRecur (x : xs) =
  if isDigit x
    then
      digitToInt x + sumDigitsRecur xs
    else sumDigitsRecur xs

sumDigitsListComp :: String -> Int
sumDigitsListComp i = sum [if isDigit x then digitToInt x else 0 | x <- i]

sumDigitsMapFilterFold :: String -> Int
sumDigitsMapFilterFold i = foldr (+) 0 (map digitToInt (filter isDigit i))