{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE ViewPatterns #-}

-- A space is used instead of `--` because Haskell's
-- standard library has no `splitOn` function :(
applyCustomerId :: String -> String
applyCustomerId name = name ++ " 23098234908"

unapplyCustomerId :: String -> Maybe String
unapplyCustomerId str = case words str of
  (name:_) -> Just name
  _ -> Nothing

pattern CustomerId :: String -> String
pattern CustomerId name <- (unapplyCustomerId -> Just name)

main = case applyCustomerId "Sukyoung" of
  CustomerId name -> putStrLn name
  _ -> putStrLn "Could not extract a CustomerID"