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Re: Why <empty-list> and <pair>? or More heresy...
- To: Jonathan.Bachrach@ircam.fr, email@example.com
- Subject: Re: Why <empty-list> and <pair>? or More heresy...
- From: firstname.lastname@example.org (Scot Dyer)
- Date: Tue, 1 Dec 92 08:41:29 PST
/// From: Jonathan Bachrach <Jonathan.Bachrach@ircam.fr>
/// Subject: Why <empty-list> and <pair>? or More heresy...
/// [...stuff deleted...]
/// It could even be argued that #F should also be used as the bottom
/// value for <list>. It seems that the real reason to want to use '() is
/// so that people can `cdr' and `car' it without first checking and that
Gack! Grand Heretic that I am, I don't want to see Dylan have NIL! This would
be to parallel one of LISP's grand mistakes by not providing a proper bottom
list distinguishable from false...
I do agree that (singleton '()) seems more in keeping with the rest of the
/// (instance? '() <list>) => #T
/// thereby making declarations easier or no need to resort to
/// (or (singleton #F) <list>)
/// I like these efficiency features, but if people want symmetry, then
/// one might consider using #F instead of '().
It doesn't seem that efficient to me. Anyway, isn't '() considered a <list>?
I think <list> is an abstract class from which both <empty-list> and <pair>
inherit. This is reason enough for me to want to leave <list>, <empty-list>
and <pair> -- different classes for different underlying representations seems
/// I actually still prefer automatic void values (changed the name to
/// avoid collision with the usual connotations of bottom value), where
/// the void value is an instance of the class and could be customized to
/// have special properties for efficiency (such as '()). Programs can
/// access the void value and use it for singleton dispatching. This
/// makes the use of a void value (such as '()) both efficient and
We're not going to get them. Let's move on.