This sounds very similar to Emacs' undo history, except Emacs doesn't implement the "window shopping" optimisation. Instead, Emacs has a command `undo-only` whi

This sounds very similar to Emacs' undo history, except Emacs doesn't implement the "window shopping" optimisation. Instead, Emacs has a command `undo-only` which is similar to `undo` except it will skip over undo-redo chains. > Thus you can use up all available memory in approx. 64 quick steps by: ... I disagree. If the editor uses a very basic implementation, then "Undo to beginning" would probably require the user to perform multiple undo steps, in which case the memory usage would be linear in the number of steps rather than exponential. If the editor supports "Undo to beginning" as a single operation, then it would be reasonable to expect a more sophisticated implementation that does it efficiently -- memory usage can be reduced by sharing the repeated sections of the undo/redo stacks, and it is possible to efficiently skip over undo-redo sequences by recording which states are identical. Exponential memory usage would be indicative of a lazy programmer rather than a fundamental issue with the GRUQ-orithm :)