You could arrange numbers in a heap according to size.

> h := heap[new](`<`, 4, 7, 19, 111, 2):

> heap[insert](17, h):

> while not heap[empty](h) do heap[extract](h); end do;
                                      111

                                      19

                                      17

                                       7

                                       4

                                       2

As for extracting them to a list, I presume that you want the list sorted (by the same boolean-valued function used by the heap). Note that, for a heap h stored in a table according to the scheme above, the element h[0] is the number of stored values while the element h[`<`] is the boolean valued function which compares/sorts them.

> h := heap[new](`>`, 4, 7, 19, 111, 2):
> sort([seq(h[i],i=1..h[0])],h[`<`]);
                              [111, 19, 7, 4, 2]

> h := (heap[new])(lexorder, greg, tony, bruno, michael):
> sort([seq(h[i],i=1..h[0])],h[`<`]);
                         [bruno, greg, michael, tony]

See here for some nice notes on efficient sorting of lists.

note: This stuff above involves heaps implemented as Maple tables. You also wrote that you wanted to implement a heap as a list. Do you really want to do that, as well, even though Maple lists are not efficient mutable data structures?

acer