code: def one(func, n=0):
      
      def _one(result):
          if _isSequenceTypeNotText(result) and len(result) > n:
              return func(result[n])
          return None
      return maybe(_one)
docs: Create a callable that applies ``func`` to a value in a sequence.
  
      If the value is not a sequence or is an empty sequence then ``None`` is
      returned.
  
      :type  func: `callable`
      :param func: Callable to be applied to each result.
  
      :type  n: `int`
      :param n: Index of the value to apply ``func`` to.