Peter Hercek wrote:
Simon Marlow wrote:
You seem to have a plan for maintaining a dynamic stack for debugging,
perhaps you could flesh out the details in a wiki page, mainly to
ensure that we're discussing the same thing?
Sure, but the plan to maintain an approximate debugging dynamic stack
depends on one thing:
The number of items (continuations) on the return stack from the
beginning of /case tick<n> of {_->e}/ to the moment when we can check
the count of items in the return stack inside /tick<n>/ is constant and
known for a given runtime version of ghc. Or variable but known for each
call individually. This is important to find out the number of return
addresses on the return stack just before the execution of /case tick<n>
of {_->e}/.
I don't fully understand what it is you mean. e.g. I don't know what "from
the beginning of /case tick<n> of {_->e}/" means.
Let me try to explain a couple of things that might (or might not!) help
clarify. We don't normally see
case tick<n> of { _ -> e }
because the byte-code generator turns this into
let
z = case tick<n> of { _ -> e }
in
z
the debugger paper explains why we do this. Anyway, the byte code for the
closure for z does this:
- if the breakpoint at <n> is enabled then stop,
- otherwise, evaluate e
i.e. it doesn't push any stack frames.
Does that help frame your question?
Cheers,
Simon
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