input: Write a function that checks if a given string `s` contains matching parentheses. The function should return `True` if all parentheses are properly matched and `False` otherwise. If the string is empty, the function should return `True`.
  assert matching_paren("()")==True
  assert matching_paren("(())")==True
  assert matching_paren("()()")==True
  assert matching_paren("(()")==False
  assert matching_paren("())")==False
  assert matching_paren("")==True
output: def matching_paren(s):
      stack = []
      for char in s:
          if char == '(':
              stack.append(char)
          elif char == ')':
              if not stack:
                  return False
              stack.pop()
      return len(stack) == 0