6 Dec
2004
6 Dec
'04
2 p.m.
Well, if you consider large word-processors like word keep a complete undo history, I would keep a document as a list of changes:
data Document = Insert Location String | Delete Location Location ...
Better to store it as a pair of the most recent state, and a list of *reversed* changes. --KW 8-) -- Keith Wansbrough <kw217@cl.cam.ac.uk> http://www.cl.cam.ac.uk/users/kw217/ University of Cambridge Computer Laboratory.