Bronze Edition Guide - True BASIC

UNDO and REDO
UNDO can be applied to:
CUT
COPY
PASTE
FUNCTION F4 (select text block)
FUNCTION F5 (copy and paste)
FUNCTION F6 (cut and paste)
DELETE
TYPING
KEEP
INCLUDE
DO….
FORMAT
UPPER
LOWER
FORMS
TBILT
The UNDO menu item shows the current action, e.g. UNDO delete.
In the case of typing, UNDO will restore the original text before CONTINUOUS typing
began. For example, suppose you type ABC anywhere on an existing line, then UNDO
will remove ABC. You can still use the back-space key to remove individual letters. You
might have typed say 20 lines of code, and when you press UNDO then all 20 lines will
be removed. To limit the amount of text in a single “UNDO typing” group, you can break
up the groups by highlighting a letter or word and then clear the highlight before carrying
on with your typing. By selecting a highlight you are effectively creating a new activity,
so the editor closes the current typing activity and opens a new activity called “Select”
and waits for you to decide what you are going to do next. If you carry on typing, then
the editor renames “Select” as “Typing”.
Each time you begin an activity such as typing, cut, copy, paste, DO FORMAT etc., the
editor takes a “photocopy” of the current program and keeps it in an internal array so that
you can return to this copy if you want to UNDO the activity. There are ten elements in
the internal array so you can use UNDO to backtrack ten times. It is unlikely that any
program will exceed 2MB so all 10 “photocopies” will only take up 20MB of memory.
Obviously you will perform more than just ten activities, so on the eleventh activity, the
first internal array is re-used. This first-in-first-out process continues indefinitely.
For example; suppose you have already done 9 different activities and you are now
typing, i.e. the tenth item in the undo list is typing. You now want to do a cut and paste
operation so your undo list will now have two more items – “cut” and “paste” as the
eleventh and twelfth activities. The internal array is limited to 10 elements so the whole
list moves up two places to allow cut and paste to occupy elements 9 and 10. Your
previous typing activity now occupies element 8. The two old elements at the top of the
list are discarded. You now decide to back track 5 places up the list with the UNDO
feature. Now you realize this is too far so you move down the list with the REDO feature
by two places, i.e. element 7. Ahead of you there are still typing, cut and paste, but you
decide that element 7 is where you want to be, so you begin typing your program again.
This typing operation will now OVER-WRITE element 8 and subsequent activities will
over-write elements 9 and 10. However, all the elements prior to element 7 will still be
preserved.