Re: Predicate for true lists

[Paul Eggert]

Eli Zaretskii wrote:
> the documentation still doesn't say that 'length' signals
> an error for anything that is not a sequence, which is what
> proper-list-p is relying on.

The proposed implementation of proper-list-p does not rely on such a signal, 
because it invokes 'length' only on nil and conses, and a cons must be either a 
proper list, a dotted list, or a circular list. Since the 'length' documentation 
specifies behavior in all these cases, the proposed implementation of 
proper-list-p does not need the 'length' documentation to also say that 'length' 
signals an error for non-sequences. (Perhaps it is a good idea to add such 
documentation for other reasons, but that's a different matter.)