Virtually infinite list box

[Morten Welinder <terra diku dk>]

I want to create a large list box/text field with ~100000 lines
in it.  It would, obviously be wasteful to construct the full
thing in memory, so I was hoping to construct it on a need-to-
see basis, i.e., only the visible parts are created.

Consider a list with 11 items, the numbers from -5 to +5.  As
you move up, the numbers -6, -7, ... get added.  As you move
down, the numbers +6, +7, ... get added.  Perhaps the numbers
that are no longer visible get removed.

Any help or pointers?

Morten