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Re: vm branch now uses vm repl by default

From: Andy Wingo
Subject: Re: vm branch now uses vm repl by default
Date: Wed, 10 Sep 2008 20:51:23 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux)


On Wed 10 Sep 2008 00:43, "Neil Jerram" <address@hidden> writes:

> I guess source information is of interest for debugging

Of course :)

> you've observed previously elsewhere that the VM doesn't yet have much
> debugging support - by which I presume you mean something like the
> traps that the evaluator has.

Oh it has some. Here are the hooks:

    vm-next-hook vm-apply-hook vm-boot-hook vm-return-hook
    vm-break-hook vm-exit-hook vm-halt-hook vm-enter-hook

They sound sufficient, but perhaps more could be added. Unless I
misunderstand what the traps do (which is likely).

> So I was just wondering if we actually _need_ any debugging support in
> the VM.

Certainly we do for debugging the VM itself. But besides that, if the VM
will be the way that people will want to run their programs, they need
good backtraces at the very least. Which implies at least source

I think the only thing that is missing at this point is procedure names
(which I haven't spent enough time figuring out how to push them down
the compilation pipeline, but the support is there), and spaghetti
stacks, which are also needed to support call/cc.

> Then another question is whether we can assume that the VM behaves
> equivalently to the evaluator.

I think that this is a precondition for merging vm to master.

> code that doesn't have side effects?

If you believe that, I've got a type system in Scotland I'd like to sell
you ;-)



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