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Re: What's the canonical way to check "alistp"?

From: Robert L.
Subject: Re: What's the canonical way to check "alistp"?
Date: Mon, 5 Mar 2018 19:17:24 +0000 (UTC)
User-agent: XanaNews/

On 3/1/2018, Drew Adams wrote:

> > What's the best way to check if every element in a list is also a list?
> Also a list or also a cons? Do you want (alistp '(()))
> to return true?  I'm guessing no.
> (defun alistp (xs)
>   "Return non-nil iff XS is a list and each element is a cons."
>   (and (listp xs)
>        (catch 'alistp
>          (dolist (x  xs) (unless (consp x) (throw 'alistp nil)))
>          t)))
> (The code should not bother to check each element if it
> finds one that is not a cons.)

(defun alistp (xs)
  (and (listp xs) (while (consp (car xs)) (pop xs)))
  (not xs))

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