> It doesn't seem possible to get what I'm looking for using the
> technique used in Binding.of_caller which is to set a trace to detect
> when we return to the caller (or is it from the caller). To do what
> I'm talking about seems to require examining the current call stack to
> get the receiver of the preceding message.
>
> It looks like the best you can do in ruby is to get a backtrace with
> Kernel#caller, or by raising and rescuing an exception, only gives
> strings describing where you were in the source, but with no access to
> the actual receiver objects.

Have a look at this article: http://eigenclass.org/hiki.rb?breakpoint 
+breaking+in+1.8.5.

I believe the new library described here may be of use to you when it  
is released.

Matthew