Add sum digits

sum_digits.hs

@@ -0,0 +1,15 @@
+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))