[discuss] Support for reverse-execution

[Michael Snyder]

Daniel Jacobowitz wrote:

> It seems to me that if we give them unique names, the logical parallel
> with existing commands may be lost.  But perhaps not.  Let's try for
> the full set:
> 	continue	reverse-continue
> 	step		reverse-step
> 	next		reverse-next
> 	stepi		reverse-stepi
> 	nexti		reverse-nexti
> 	until		reverse-until
> 	advance		reverse-advance
> 	finish		reverse-finish
> 
> I think that's the full set of reversible commands. 

reverse-return?  <shudder>

 > Which of them
> don't work?  I agree that reverse-next is a little weak, but everything
> else seems OK.  And we aren't limited to one name for things!  We could
> add "prev" as an alias to "next" if you like that.

I like these, as being the most informative, with shorter and perhaps
more mnemonic versions  (such as prev) as aliases.  Eli, you should
like these because they're somewhat self-documenting (not that we'd
want to skimp on the real docs)

> We could use r-prefixed commands.  I don't think that helps much, since
> we're already planning to offer abbreviations like "rs" and "rni", but
> they're my second-favorite choice:
>   rcontinue, rstep, rnext, rstepi, rnexti, runtil, radvance, rfinish
> 
> We could use "backwards" for everything.  Those mostly sound right,
> except that backwards has some unfortunate connotations. 

What if, in addition to what you describe above, we defined
a *prefix* command "backwards" -- which would simply modify
the other commands, eg. "backwards continue" (no hyphen)
would call continue with whatever parameters would make it
proceed backwards (or would call reverse-continue, or whatever).

Maybe this is too many ways to do the same thing, but
it would cost us essentially nothing...

Furthermore, we could implement as many of these interfaces
as we wish, hidden in "maintainer mode" or something, and
try them out -- see how we like them.

 > I think
> that advance and finish come out as particularly odd:
>   backwards-continue, backwards-step, backwards-next, backwards-stepi,
>   backwards-nexti, backwards-until, backwards-advance, backwards-finish
> 
> This one's kind of nice, we could use suffixes instead.  But
> next-backwards is very awkward:
>   continue-backwards, step-backwards, next-backwards, stepi-backwards,
>   nexti-backwards, until-backwards, advance-backwards, finish-backwards
>