>From b30eaba87be980c8fbaea3c124c3cadd9aec6fe0 Mon Sep 17 00:00:00 2001
From: Damien Cassou <damien@cassou.me>
Date: Mon, 17 Apr 2017 11:01:39 +0200
Subject: [PATCH] Add seq-set-equal to test for set equality

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

* test/lisp/emacs-lisp/seq-tests.el (test-seq-set-equal): Add test for
  seq-set-equal.
---
 doc/lispref/sequences.texi        | 28 ++++++++++++++++++++++++++++
 etc/NEWS                          |  3 +++
 lisp/emacs-lisp/seq.el            |  8 ++++++++
 test/lisp/emacs-lisp/seq-tests.el | 25 +++++++++++++++++++++++++
 4 files changed, 64 insertions(+)

diff --git a/doc/lispref/sequences.texi b/doc/lispref/sequences.texi
index 93e8fa8..2f6fb1d 100644
--- a/doc/lispref/sequences.texi
+++ b/doc/lispref/sequences.texi
@@ -792,6 +792,34 @@ Sequence Functions
 
 @end defun
 
+@defun seq-set-equal sequence1 sequence2 &optional testfn
+This function checks whether every element of @var{sequence1} also
+appears in @var{sequence2} and if every element of @var{sequence2}
+also appears in @var{sequence1}.  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 '(a b c) '(c b a))
+@result{} t
+@end group
+@group
+(seq-set-equal '(a b c) '(c b))
+@result{} nil
+@end group
+@group
+(seq-set-equal '("a" "b" "c") '("c" "b" "a"))
+@result{} t
+@end group
+@group
+(seq-set-equal '("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
diff --git a/etc/NEWS b/etc/NEWS
index 76c9dbc..9b6c89d 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -874,6 +874,9 @@ instead of its first.
 
 * Lisp Changes in Emacs 26.1
 
+** New function 'seq-set-equal' to check if every element of LIST1 also
+appears in LIST2 and if every element of LIST2 also appears in LIST1.
+
 +++
 ** Emacs now supports records for user-defined types, via the new
 functions 'make-record', 'record', and 'recordp'.  Records are now
diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
index 10de248..40f2988 100644
--- a/lisp/emacs-lisp/seq.el
+++ b/lisp/emacs-lisp/seq.el
@@ -355,6 +355,14 @@ seq-sort-by
                 e))
             sequence))
 
+(cl-defgeneric seq-set-equal (sequence1 sequence2 &optional testfn)
+  "Return true if SEQUENCE1 and SEQUENCE2 have same elements.
+I.e., if every element of SEQUENCE1 also appears in SEQUENCE2 and if
+every element of SEQUENCE2 also appears in SEQUENCE1.
+Equality is defined by TESTFN if non-nil or by `equal' if nil."
+  (and (seq-every-p (lambda (item1) (seq-contains sequence2 item1 testfn)) sequence1)
+       (seq-every-p (lambda (item2) (seq-contains sequence1 item2 testfn)) sequence2)))
+
 (cl-defgeneric seq-position (sequence elt &optional testfn)
   "Return the index of the first element in SEQUENCE that is equal to ELT.
 Equality is defined by TESTFN if non-nil or by `equal' if nil."
diff --git a/test/lisp/emacs-lisp/seq-tests.el b/test/lisp/emacs-lisp/seq-tests.el
index 788524b..9cc54d8 100644
--- a/test/lisp/emacs-lisp/seq-tests.el
+++ b/test/lisp/emacs-lisp/seq-tests.el
@@ -197,6 +197,31 @@ test-sequences-oddp
     (should (seq-every-p #'identity seq))
     (should (seq-every-p #'test-sequences-evenp seq))))
 
+(ert-deftest test-seq-set-equal ()
+  (with-test-sequences (seq1 '(1 2 3))
+    (should (seq-set-equal seq1 seq1))
+    (should (seq-set-equal seq1 seq1 #'eq))
+
+    (with-test-sequences (seq2 '(3 2 1))
+      (should (seq-set-equal seq1 seq2))
+      (should (seq-set-equal seq2 seq1))
+      (should (seq-set-equal seq1 seq2 #'eq))
+      (should (seq-set-equal seq2 seq1 #'eq)))
+
+    (with-test-sequences (seq2 '(3 1))
+      (should-not (seq-set-equal seq1 seq2))
+      (should-not (seq-set-equal seq2 seq1))))
+
+  (should (seq-set-equal '("a" "b" "c")
+                         '("c" "b" "a")))
+  (should-not (seq-set-equal '("a" "b" "c")
+                             '("c" "b" "a") #'eq))
+  (should-not (seq-set-equal '(("a" 1) ("b" 1) ("c" 1))
+                             '(("c" 2) ("b" 2) ("a" 2))))
+  (should (seq-set-equal '(("a" 1) ("b" 1) ("c" 1))
+                         '(("c" 2) ("b" 2) ("a" 2))
+                         (lambda (i1 i2) (equal (car i1) (car i2))))))
+
 (ert-deftest test-seq-empty-p ()
   (with-test-sequences (seq '(0))
     (should-not (seq-empty-p seq)))
-- 
2.9.3