Wild and Crazy idea for interactivity

[Jane Anderson/Monty Zukowski]

I was just reading through the Lout design document and noticed that
parsing happens lazily, as processing needs it.  Suppose I could use
"Recoverable Virtual Memory" to save and restore the actual contents of
memory for Lout.  This would give me a way to say "go back to the state you
were in right before reading this paragraph."

So as a user was editing a certain paragraph, I could restore memory to
that place before that paragraph was read, then change the input stream to
have the new paragraph read in and parsed.  Then I would let it run until
the PS for that page was generated.  I could then render the PS to the
screen for the user.

This would hopefully be able to make changes processed at somewhat
interactive speeds.  Then optimizations could be pursued such as only
re-rendering the lines that actually changed.  And fun stuff like mapping a
text selection back to the original source, etc.

Basically the RVM gives me a cache so I can fast forward Lout to the
correct state before processing a specific page.  Maybe that would be
implementable in another manner too?

So is this a possible way to get some interactivity or am I too clever for
my own good and overlooking something fundamental?

Monty