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Re: Elisp development news

From: Neil Jerram
Subject: Re: Elisp development news
Date: 09 Jan 2002 20:33:35 +0000
User-agent: Gnus/5.0808 (Gnus v5.8.8) Emacs/20.7

>>>>> "Marius" == Marius Vollmer <address@hidden> writes:

    Marius> Neil Jerram <address@hidden> writes:
    >> I don't see why it's useful for the Elisp nil value to satisfy
    >> Scheme's `symbol?'.

    Marius> What about 

    Marius>     (setq big-rivers '(amazonas nil ruhr))

What about it? :-)  This is Elisp code.  Obviously we have to make
sure that all Elisp code executes as expected, which includes this
expression and the fact that (symbolp nil) => t.  But it has no
relevance a priori to how Scheme sees the Elisp nil value.

    Marius> Beyond it's uses a the empty list and the false value, nil is also a
    Marius> symbol and both sides need to recognize it as such.

Actually, the nil value can't be a Scheme symbol, at least not the one
with name `nil'.  If it was, unsuspecting Scheme code could be tricked
up by this:

(if 'nil #t #f)
=> #t              ; R5RS
=> #f              ; Guile, if 'nil evaluates to the Elisp nil value

IMO this would be an unacceptable violation of R5RS.


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