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From: | Paul Eggert |
Subject: | Re: Predicate for true lists |
Date: | Sat, 7 Jul 2018 01:41:38 -0700 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 |
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.)
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