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Re: Predicate for true lists

From: Basil L. Contovounesios
Subject: Re: Predicate for true lists
Date: Mon, 04 Jun 2018 15:46:30 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

Stefan Monnier <address@hidden> writes:

>> address@hidden list-true-p object
>> +This function returns @code{t} if OBJECT is a true list, @code{nil}
>> +otherwise.  In addition to satistying @code{listp}, a true list is
>> +neither circular nor dotted.
> I think this function's true name is `list-proper-p` or `proper-list-p`.
> At least I've always heard it talked about as "a proper list vs
> a non-proper list".

That was my impression as well, but "(elisp) Cons Cells" states:

   Also by convention, the CDR of the last cons cell in a list is ‘nil’.
   We call such a ‘nil’-terminated structure a “true list”.

The documentation of functions 'append' in "(elisp) Building Lists" and
'vconcat' in "(elisp) Vector Functions" similarly refer to "true" lists.

If "proper" is the more common/preferred term, I should probably update
those nodes in addition to my patch, right?

> As for `cdr` vs CDR.  The all-caps version is a metavariable referring
> to something which we happened to call CDR.  E.g.
>     Foo takes the form (CAR . CDR) where CDR is blabla.

Right, but I see no such destructuring/metasyntax in the Elisp manual.
Both "(elisp) Cons Cells" and "(elisp) Cons Cell Type", for example,
refer directly to the CAR and CDR slots of a cons cell, without first
illustrating their structure.  Is that OK?



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