readInt :: String -> Int
readInt = read

splitBy :: Char -> String -> [String]
splitBy _ "" =  []
splitBy ch s =  let (l, s') = break (== ch) s
                in  l : case s' of
                        []      -> []
                        (_:s'') -> splitBy ch s''

hasDelimiter :: String -> Bool
hasDelimiter text = length text > 2 && 2 == (length . takeWhile (==True) $ zipWith (==)  "//" text)

delimiter :: String -> Char
delimiter text
  | hasDelimiter text = text !! 2
  | otherwise         = '\n'


calc :: String -> Int
calc text = sum . map readInt . numbers . body $ text
            where numbers   = splitBy (delimiter text)
                  body text = if hasDelimiter text then drop 3 text else text