Posit: Unlimited "Undo" in fP?

[Bruce Easton]

I wrote Thursday, July 26, 2007 2:22 PM:
[..]
> 
> OK, for the scenario of keeping track of changes @wlf during the 
> same session prior to saving a record where I had suggested writing 
> to a separate file,
> 
> 1. Session
> 2. Field#
> 3. Seq#
> 4. Value at Seq#
> 5. maybe ScreenID?,
> 6. maybe Posted?
> 
> if that were applied to all the updatable fields for a given screen, 
> then it seems that not only could it be used in the program for 
> un-do, but, depending on how the maintenance of the history file 
> is handled, it could be used once out of the record (even if 
> ungracefully) for the purpose of producing as last "draft" of a 
> record.  (I would only update a session's set of history records 
> once the record is saved - using field 6 above.  That way if I 
> looked at the records and that was empty, then it should indicate 
> that there were draft changes that for some unknown reason, were 
> not saved.)
> 
[..]

But I would think to produce a historical series of "last drafts," that 
is easy to follow, you might need to write out an initial state 
record in @update prior to any field events.

Bruce

Bruce Easton
STN, Inc.