back/forward confined to one stack

[Charles Hartman]

I'm positively childishly pleased to report that my simple  
implementation of a history-list for a single stack or substack  
works. It confines itself to that stack alone (unlike the Rev- 
internal commands relevant to "recent" -- but thanks to Jacque for  
her suggestions that made me learn more about those). Assuming that  
each card in the relevant stack has a Back button whose mouseUp  
handler just sends the command 'backButton' and a Forward button that  
sends 'forwardButton', the handler's in the stack's script that I've  
copied below seem to do the trick.

I don't know if anybody else needs this -- or if, as I'd be glad to  
hear, there's a better way to do it. It turned out to be a pretty  
design problem; the crux is what to do when the user navigates to  
card *not* using the Back or Forward buttons. In that case I've opted  
for deleting everything in the list after the present "Ptr" position.  
This has the disadvantage of making some visited cards not accessible  
through "Back". (Visit Able then Baker then Charlie, then go back to  
Baker, then visit Delta. Charlie is not in the history path any  
more.) Getting around that requires, as far as I can see, adding  
every visit to every card (through a button or not) to the list, and  
keeping a potentially very complicated tree-based set of pointers to  
it. The only complete implementation of *that* kind of history I know  
of is the thorough, branch-preserving Undo facility of MOTU's Digital  
Performer. Certainly beyond me -- so it's a good thing it's beyond my  
needs.

Charles

======== handlers for script of stack to be "historicized"  
=================

global gHistList, gHistPtr, gFromButton

on preOpenStack
   put empty into gHistList
   put 0 into gHistPtr
   put false into gFromButton
end preOpenStack

on backButton
   if gHistPtr > 1 then
     put true into gFromButton
     subtract 1 from gHistPtr
     put line gHistPtr of gHistList into tDest
     go to tDest
   end if
end backButton

on forwardButton
   put the number of lines of gHistList into tLast
   if gHistPtr < tLast then
     put true into gFromButton
     add 1 to gHistPtr
     put line gHistPtr of gHistList into tDest
     go to tDest
   end if
end forwardButton

on preOpenCard
   if not gFromButton then
     repeat with n = the number of lines of gHistList down to  
gHistPtr + 1
       delete line n of gHistList
     end repeat
     put the name of this card & return after gHistList
     add 1 to gHistPtr
   end if
   put false into gFromButton
   if exists(btn "Back") then
     disable btn "Back"
     if gHistPtr > 1
     then enable btn "Back"
   end if
   if exists(btn "Forward") then
     disable btn "Forward"
     if gHistPtr < the number of lines of gHistList
     then enable btn "Forward"
   end if
end preOpenCard