Sorting a list of lists in the order of ascending length

Hi

I need all subsets of a list in the order of ascending length of the subsets. 

Thus I wrote a predicate 

  generate_subset(+List, -SubList) that generates a SubList of List 

and that is also used for other purposes, and a variant of insertion sort

  sort_list_of_lists_in_ascending_length(+ListOfLists, -SortedListOfList) that sorts ListOfLists into SortedListOfList 

and then called 

  findall(SubList, generate_subset(List, SubList), SubLists), sort_list_of_lists_in_ascending_length(SubLists, SortedSubLists)

This works quite nicely and efficiently, but nevertheless I wonder whether there isn't a simpler way to perform this operation. 

Regards.

   --- nef