Throw and catch, implications for error recovery

[Derek Peschel]

Hi everybody,

Neil Jerram explained some features of the Guile debugging framework and
then suggested I send further questions to guile-devel.  We talked about
error recovery as a desirable feature -- being able to continue a
computation in some way after it hits an error.  The error may be caused
by the computation or by running an "eval" or "tweak" command.  Last I
checked, no recovery is possible in either case.

Presumably the upward-only implementation of throw and catch is the
problem (or part of it).  Is that true?  Is there an easy rule for
determining which stack frames become non-recoverable?  If that's too
vague a question, I can send specific examples, though I don't have the
mental model to determine the state of the system for each example.
(What continuations exist and their contents, which continuations have
access to other continuations, other data like saved error data, etc.)

Thanks,

-- Derek