docs: def addpattern(base_func):
      """Decorator to add a new case to a pattern-matching function, where the new case is checked last."""
      def pattern_adder(func):
          @_coconut.functools.wraps(func)
          @_coconut_tco
          def add_pattern_func(*args, **kwargs):
              try:
                  return base_func(*args, **kwargs)
              except _coconut_MatchError:
                  raise _coconut_tail_call(func, *args, **kwargs)
          return add_pattern_func
      return pattern_adder