undo (was Re: Why does Dynamic Typing really matter?!?)

[Edward K. Ream]

> Actually, Leo might make this possible.  The text is naturally divided
into
> trees and subtrees, so specifying a subtree in which to do the undo would
be
> easy.

However, Leo's clone features can have any change affect arbitrarily many
nodes (vnodes) in a tree.  One could restrict operations to a list of
underlying shared text (list of tnodes), but that hardly seems like it would
be natural.

My own experience is that restricting the range of operations (e.g., to a
subtree, or selected text) is usually what is wanted.  Messing with flexible
undo seems both hard and not all that useful.  YMMV.

Doesn't Photoshop have some kind of flexible undo?  If so, I would study
their model carefully.

Edward
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Edward K. Ream   email:  edream at tds.net
Leo: Literate Editor with Outlines
Leo: http://personalpages.tds.net/~edream/front.html
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