You can also have a look at the Iterator DP in the Smalltalk companion  
they have  an hisotrystream to manipulate commands
and do undo.
On Apr 29, 2008, at 7:36 PM, itsme213 wrote:

> I have commands that I would like to make undoable. Is it possible  
> to wrap
> the commands within an "undoable" environment as suggested in
> http://www.ceteva.com/forum/viewtopic.php?t=17
>
> I imagine something like this (but wouldn't know where to start):
>
> A>>setFoo: aFoo
>    Undoable newOn: [ foo := aFoo ]
>
> A>>setBar: aBar
>    Undoable newOn: [ bar := aBar ]
>
> a := A new foo: 0; bar: 0; yourself.
> a setFoo: 5.
> a setBar: 10.
> Undoable undo. "a bar == 0"
> Undoable undo. "a foo == 0"
> Undoable redo. "a foo == 10"
>
> Thanks - Sophie
>
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