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Re: Variables and the evaluator


From: Andy Wingo
Subject: Re: Variables and the evaluator
Date: Sat, 14 Jan 2012 16:37:15 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux)

Hi,

Sorry, forgot to respond to another bit on this subtopic:

On Sat 14 Jan 2012 16:28, Andy Wingo <address@hidden> writes:

> On Sun 08 Jan 2012 21:39, Mark H Weaver <address@hidden> writes:
>
> >> More importantly, is there any guarantee that mutable lexicals will
> >> continue to be represented as variable objects in future native code
> >> compilers?  Do we want to commit to supporting this uniform
> >> representation in all future compilers?
> >
> > I don't know that we should commit to it externally, but internally it's
> > OK.  If we did have to commit to it externally even that would be OK, as
> > I don't think it will change.
>
> You may be right, but committing to a uniform representation makes me
> very uncomfortable.  I can imagine several clever ways to represent
> mutable free variables in a native compiler that don't involve separate
> variable objects for each variable.

In general, they all involve a storage location that is a word wide.
Variables are tagged storage locations, nothing more.  They are a good
choice for mutable values.  They are like Chez Scheme's or Racket's
boxes.

I have no qualms about variables here.

Andy
-- 
http://wingolog.org/



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