From: malcolm.arthur.mclean@gmail.com   
      
   On Sunday, 3 April 2022 at 14:26:22 UTC+1, oot...@hot.ee wrote:   
   >   
   > Storing whole program state is pointlessly memory consuming and diffing   
   whole program state is pointlessly expensive.   
   > More usual is to make all actions to be required to record their reverse   
   actions.   
   >   
   > So when action is done then reverse action is stored to undo stack and redo   
   stack is cleaned.   
   > Undo then means that reverse action is done and removed from undo stack and   
   action is stored to redo stack.   
   > Redo then means that action is done and removed from redo stack and reverse   
   action is stored to undo stack.   
   >   
   > That takes designing (and testing) your commands/actions/operations more   
   carefully.   
   > But that is anyway not bad at all in the long run.   
   >   
   I decided to knock something up anyway.   
   I just diff by finding the changed section. It will be inefficient if the user   
   makes an edit which moves   
   an item from the start of the string to the end, which is the most likely   
   bad-case scenario. But it's   
   O(N) in text size.   
   The other question is whether there will be many applications which can   
   cheaply stringify their   
   state. This approach makes sense for Crossword Designer, because the program   
   state is just   
   a crossword, which is 15x15 bytes for the grid and up to about a hundred short   
   strings for the clues.   
   But how many other programs have those characteristics I don't know.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)