code: def _serialize_argument(rargname, value, varprops):
      
      _argument = '{rargname}: {value}{props}'
      if rargname == CONSTARG_ROLE:
          value = '"{}"'.format(value)
      props = ''
      if value in varprops:
          props = ' [ {} ]'.format(
              ' '.join(
                  [var_sort(value)] +
                  list(map('{0[0]}: {0[1]}'.format,
                           [(k.upper(), v) for k, v in varprops[value]]))
              )
          )
          del varprops[value]  # only print props once
      return _argument.format(
          rargname=rargname,
          value=str(value),
          props=props
      )
docs: Serialize an MRS argument into the SimpleMRS format.