On Sat, Jun 08, 2002 at 02:29:53PM -0400, Dan Sugalski wrote: > There's more than just exception handlers going on the control stack. > Anything that needs rolling back or undoing (like localized variables > or scope entry) will have an undo marker put on the control stack > that gets called when we pop its entry off the control stack. It's an > easy way to remember overwritten values--you put an "overwritten" > entry on the control stack with the old value, and we restore it when > we pop the entry off the stack.
With co-routines and callcc, function start and end are not always properly nested. For instance, you can start a co-routine, enter a function, run the co-routine until it ends and then exit the function. Or you can capture the current continuation inside a function and resume it until it exits the function, and then resume it again. So I don't think pushing undo markers on the control stack will work. Maybe we should implement something like Scheme's dynamic-wind. (See ftp.cs.indiana.edu/pub/scheme-repository/doc/standards/june-92-meeting.ps.gz and http://groups.google.com/groups?selm=izvhr5y4jy.fsf%40ux01.CS.Princeton.EDU for two differents implentations of dynamic-wind.) -- Jero;e
