lexicographic list comparison

[Sam Steingold <sds@gnu.org>]

Hi,

What do you do when sorting a list of lists of numbers?

There does not appear to be a standard comparison function like
--8<---------------cut here---------------start------------->8---
(defun lexicographic-compare-lists (l1 l2 &optional lessp)
  "lexicographic list comparison"
  (unless lessp
    (setq lessp #'<))
  (or (null l2) (null l1)
      (funcall lessp (car l1) (car l2))
      (and (not (funcall lessp (car l2) (car l1)))
           (lexicographic-compare-lists (cdr l1) (cdr l2) lessp))))
--8<---------------cut here---------------end--------------->8---

[[[It appears that it is less critical for strings because one can do
--8<---------------cut here---------------start------------->8---
(sort list-of-lists-of-strings
      (lambda (l1 l2) (string< (string-join l1) (string-join l2))))
--8<---------------cut here---------------end--------------->8---
instead of
--8<---------------cut here---------------start------------->8---
(sort list-of-lists-of-strings
      (lambda (l1 l2) (lexicographic-compare-lists l1 l2 #'string<)))
--8<---------------cut here---------------end--------------->8---
even though it conses for each comparison(!)]]]

Or maybe sorting lists of lists is just such a rare op that no one has
ever encountered it before me? ;-)

Thank you.

-- 
Sam Steingold (https://aphar.dreamwidth.org/) on darwin Ns 10.3.2113
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