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

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

[Kaushal Modi]

Hello,

I wish something like alistp existed..

What's the best way to check if every element in a list is also a list?

Thanks.
-- 

Kaushal Modi

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

[Kaushal Modi]

On Thu, Mar 1, 2018 at 10:21 AM Kaushal Modi <kaushal.modi@gmail.com> wrote:

> What's the best way to check if every element in a list is also a list?
>

I don't know if there's a more concise way.. but this seems like a good way:

(if (eq 0 (cl-count-if (lambda (el) (not (listp el))) MY-VAR)) ..)
-- 

Kaushal Modi

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

[Dmitry Gutov]

On 3/1/18 5:29 PM, Kaushal Modi wrote:
> On Thu, Mar 1, 2018 at 10:21 AM Kaushal Modi <kaushal.modi@gmail.com> wrote:
> 
>> What's the best way to check if every element in a list is also a list?
>>
> 
> I don't know if there's a more concise way.. but this seems like a good way:
> 
> (if (eq 0 (cl-count-if (lambda (el) (not (listp el))) MY-VAR)) ..)

(seq-every-p #'consp alist) if we're checking for an alist.

Use #'listp otherwise.

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

[Kaushal Modi]

On Thu, Mar 1, 2018 at 10:34 AM Dmitry Gutov <dgutov@yandex.ru> wrote:

>
> (seq-every-p #'consp alist) if we're checking for an alist.
>
> Use #'listp otherwise.


Thanks!
-- 

Kaushal Modi

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

[Drew Adams]

> 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.)

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

[Robert L.]

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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