Undo / redo

[rr-]

Self-explanatory.

A basic idea for implementation is to keep a list of text removals and text insertions. Each operation that changes text would produce two artifacts: what to do with the current state to reach the target state, and what to do with the target state to reach the current state.

Traversing the list shouldn't remove states, i.e. do not make this a stack. Otherwise redoing operations won't be possible.

On the other hand, appending states to the list should cut off the current branch:

• Current undo buffer state:
  Operation 1 - Operation 2 - Operation 3
• undo happens
  Current undo buffer state:
  Operation 1 - Operation 2 - Operation 3
• undo happens
  Current undo buffer state:
  Operation 1 - Operation 2 - Operation 3
• the document is edited
  Current undo buffer state:
  Operation 1 - Operation 4 (operation 2 and 3 were freed from the memory)