Add `value<` (bug#69709)

It's a general-purpose polymorphic ordering function, like `<` but
for any two values of the same type.

* src/data.c (syms_of_data): Add the `type-mismatch` error.
(bits_word_to_host_endian): Move...
* src/lisp.h (bits_word_to_host_endian): ...here, and declare inline.
* src/fns.c (Fstring_lessp): Extract the bulk of this function to...
(string_cmp): ...this 3-way comparison function, for use elsewhere.
(bool_vector_cmp, value_cmp, Fvaluelt): New.
* lisp/emacs-lisp/byte-opt.el (side-effect-free-fns, pure-fns):
Add `value<`, which is pure and side-effect-free.
* test/src/fns-tests.el (fns-value<-ordered, fns-value<-unordered)
(fns-value<-type-mismatch, fns-value<-symbol-with-pos)
(fns-value<-circle, ert-deftest fns-value<-bool-vector): New tests.
* doc/lispref/sequences.texi (Sequence Functions):
* doc/lispref/numbers.texi (Comparison of Numbers):
* doc/lispref/strings.texi (Text Comparison):
Document the new value< function.
* etc/NEWS: Announce.

1 files changed, 10 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 696d744e342..73ffff9f2d3 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1760,6 +1760,16 @@ precedence over the variable when present.
 Mostly used internally to do a kind of topological sort of
 inheritance hierarchies.
 
++++
+** New polymorphic comparison function 'value<'.
+This function returns non-nil if the first argument is less than the
+second.  It works for any two values of the same type with reasonable
+ordering for numbers, strings, symbols, bool-vectors, markers, buffers
+and processes.  Conses, lists, vectors and records are ordered
+lexicographically.
+It is intended as a convenient ordering predicate for sorting, and is
+likely to be faster than hand-written Lisp functions.
+
 ** New function 'sort-on'.
 This function implements the Schwartzian transform, and is appropriate
 for sorting lists when the computation of the sort key of a list