[m-dev.] spypoints in external debugger

[Gregory Daniel Denehy]

Hi,

I have two questions in regards to adding spypoints to the external
debugger interface that are mainly directed to Fergus and Erwan.

The first is about return types.  I have implemented some changes to the
interface that allow breakpoints to be added by using the procedures from
mercury_trace_spy.h in much the same manner as the internal debugger
does.  The debugger interface needs to reply to an 'add_breakpoint' 
request with either an 'ok.' if the request was successful, or some other
reply if the request could not be matched with an existing procedure or
the request was ambiguous.  My question concerns how this should be done.
Returning an 'ok.' term is obvious to me, but I'm unsure whether the other
cases should return a term of their own, eg 'no_such_procedure.', or
return an error term.  In my opinion, returning an error should not be
used for returning information.  However, the internal debugger prints
messages for these to stderr.  I simply needs some clarification about
which approach I should be using.

My second question is concerned with how the spypoints themselves are to
implemented.  I'm able to add spypoints to the spypoint table, however,
I'm unable to get the execution to stop when it reaches a spypoint.  What
needs to be done here?

Thanks

Greg


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