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Re: The dynamic stack
From: |
Andy Wingo |
Subject: |
Re: The dynamic stack |
Date: |
Wed, 07 Mar 2012 10:51:58 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux) |
Hi Noah,
On Wed 07 Mar 2012 07:05, Noah Lavine <address@hidden> writes:
>>> The “dynwind stack” actually (I misread it the first time.)
>>
>> Yes, it did have this name before. (More often, "the wind list".) But
>> since "dynwind" is overloaded so much (dynamic-wind operator, <dynwind>,
>> scm_dynwind_*), and the dynamic stack can have other things on it like
>> prompts, I thought it best to give it a new name.
>
> I see your point about the old name, but I find the new name
> confusing. What about the stack that holds regular program variables
> and temporaries? That is also dynamic, so at first I thought you were
> referring to that. I didn't know what was going on until this email.
It's a good question!
The essential difference is that lookup on the VM stack is static --
things are always at known locations. That's what lexical scoping gives
us. Lookup on the dynamic stack is dynamic: e.g. "what's the nearest
prompt with tag FOO", "what are the dynamic-wind expressions within that
extent", etc.
In an ideal world, we'd probably use the same stack for both purposes,
as C++ does (AFAIU). The reason that we don't is that the scm_dynwind_*
API manipulates the dynwind stack from outside of the VM.
Cheers,
Andy
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