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Re: please help concerning specpdl
From: |
Davis Herring |
Subject: |
Re: please help concerning specpdl |
Date: |
Tue, 14 Dec 2010 16:14:50 -0800 (PST) |
User-agent: |
SquirrelMail/1.4.8-5.el5_4.10.lanl3 |
> Why let-binding-variables are memorized exactly here and not elsewhere ?
Flet memorizes their old values on the stack; when it returns (or
otherwise is exited), the old values are copied back, so they can't be
needed beyond the lifetime of that stack frame.
> why the do-while is good in this case, and not simply brackets?
So that the whole thing is one statement that needs a ;, just like a
normal function call. If it were brackets, you couldn't do
if(x) SAFE_ALLOCA(...);
else y=x;
> I see that inside unbind_to, the symbols are unbounded 1 by one. Why the
> specpdl_ptr is not decremented directly with count ?
Because you need to do something with each record: restore old values for
symbols, call functions registered with record_unwind_protect(), etc.
> Probably because unbind_to is called from lisp code by (throw 'symbol
> value), and specpdl_ptr must decrement 1 by 1 until the 'symbol is dound
> on the stack ?
catch-tags are searched separately: see struct catchtag.
> Apart from (throw ... ), is which other situation unbind_to is called ?
The other important one is Fsignal (quit and other errors).
> I see that GCPROx macros are used to protect the variables of type Lisp
> Object on the stack of C code (that the compiler creates), not to protect
> the lisp objects in specpdl. The GCPRO protection is against the algorthm
> of conservative stack. Am I right ?
I believe the GCPRO draws the attention of the stack checker to those Lisp
objects to make sure that they're not collected.
Davis
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