On 4-Nov-09, at 9:26 AM, Eliot Miranda wrote:

> So I think the needs aren't for good print strings.  The needs are  
> actually for much higher-level tools that allow one to
> - compare object graphs with a richer result than merely equal or  
> not, i.e. explore the comparison
> - trace the evolution of object graphs during computation, ideally  
> supporting evolution in lock-step of more than one graph, perhaps  
> simply allowing one to record the sequence of evolutions such that  
> one can compare one trace to another
>
> How general is this kind of thing?  Do others find themselves  
> looking at this kind of thing often?  I fear not.

It sounds like you want something akin to omniscient debugging. (See http://www.LambdaCS.com/debugger/debugger.html) 
. If the VM were instrumented to log all state changes, a debugger- 
like tool could visualize the changing state of the image over time.  
For your purposes, you'd just have to compare the logs to find out  
where they diverged. IIRC John McIntosh did something a bit like this  
for the Mac VM. It might serve as a starting point, anyway.

Colin