Add seq-set-equal-p to test for set equality

* lisp/emacs-lisp/seq.el (seq-set-equal-p): Add function to compare
  two lists as if they were sets.

* test/lisp/emacs-lisp/seq-tests.el (test-seq-set-equal-p): Add test
  for seq-set-equal-p.

1 files changed, 27 insertions, 0 deletions

diff --git a/doc/lispref/sequences.texi b/doc/lispref/sequences.texi
index 93e8fa8a5fa..c7cf9f5e1af 100644
--- a/doc/lispref/sequences.texi
+++ b/doc/lispref/sequences.texi
@@ -792,6 +792,33 @@ it is a function of two arguments to use instead of the default @code{equal}.
 
 @end defun
 
+@defun seq-set-equal-p sequence1 sequence2 &optional testfn
+This function checks whether @var{sequence1} and @var{sequence2}
+contain the same elements, regardless of the order. If the optional
+argument @var{testfn} is non-@code{nil}, it is a function of two
+arguments to use instead of the default @code{equal}.
+
+@example
+@group
+(seq-set-equal-p '(a b c) '(c b a))
+@result{} t
+@end group
+@group
+(seq-set-equal-p '(a b c) '(c b))
+@result{} nil
+@end group
+@group
+(seq-set-equal-p '("a" "b" "c") '("c" "b" "a"))
+@result{} t
+@end group
+@group
+(seq-set-equal-p '("a" "b" "c") '("c" "b" "a") #'eq)
+@result{} nil
+@end group
+@end example
+
+@end defun
+
 @defun seq-position sequence elt &optional function
   This function returns the index of the first element in
 @var{sequence} that is equal to @var{elt}.  If the optional argument