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Re: Elisp development news

From: Marius Vollmer
Subject: Re: Elisp development news
Date: 02 Jan 2002 22:50:42 +0100
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.1

Neil Jerram <address@hidden> writes:

> You've now persuaded me that Jim's approach is functionally preferably
> to mine.

Ok, so let's go and implement Jim's approach.  (That is, let's put it
on the TODO list... :-/ )

> [...]
> The concern is that I'm still worried about the performance impact of
> managing multiple false values and multiple end of list values.  I
> know that Jim suggests a solution in his proposal, but am not
> convinced that it will not affect performance.  What do you think
> about Jim's suggestion here, and do you have any other thoughts on
> implementation and performance?

It will affect performance, but I expect it to yield only a small
performance hit.  I expect that, at worst, a test for falseness will
turn from a comparison with a constant to two comparisons with one
constant and one global variable.

> The question is whether the Elisp nil value should be distinct from
> the `nil' symbol.  I presume yes (from your argument below) but just
> wanted to check.  If yes, I further presume that the nil value should
> be a new SCM_MAKIFLAG value; is that right?

Yes, that what I thought so far.  However, it might be better to make
nil a real symbol (i.e., satisfying our current SCM_SYMBOLP) and
somehow play tricks with the heap segments to still get a constant
value for the nil value (but I wouldn't know off-hand how to do this

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