Add seq-intersection and seq-difference to the seq library

* lisp/emacs-lisp/seq.el (seq-intersection, seq-difference): New
functions.

* test/automated/seq-tests.el: Add tests for seq-intersection and
seq-difference.

* doc/lispref/sequences.texi: Add documentation for seq-intersection
and seq-difference.

1 files changed, 28 insertions, 1 deletions

diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
index c5f5906e7e5..6f7f3c46e2a 100644
--- a/lisp/emacs-lisp/seq.el
+++ b/lisp/emacs-lisp/seq.el
@@ -4,7 +4,7 @@
 
 ;; Author: Nicolas Petton <nicolas@petton.fr>
 ;; Keywords: sequences
-;; Version: 1.3
+;; Version: 1.4
 ;; Package: seq
 
 ;; Maintainer: emacs-devel@gnu.org
@@ -240,6 +240,26 @@ negative integer or 0, nil is returned."
         (setq seq (seq-drop seq n)))
       (nreverse result))))
 
+(defun seq-intersection (seq1 seq2 &optional testfn)
+  "Return a list of the elements that appear in both SEQ1 and SEQ2.
+Equality is defined by TESTFN if non-nil or by `equal' if nil."
+  (seq-reduce (lambda (acc elt)
+                (if (seq-contains-p seq2 elt testfn)
+                    (cons elt acc)
+                  acc))
+              (seq-reverse seq1)
+              '()))
+
+(defun seq-difference (seq1 seq2 &optional testfn)
+  "Return a list of th elements that appear in SEQ1 but not in SEQ2.
+Equality is defined by TESTFN if non-nil or by `equal' if nil."
+  (seq-reduce (lambda (acc elt)
+                (if (not (seq-contains-p seq2 elt testfn))
+                    (cons elt acc)
+                  acc))
+              (seq-reverse seq1)
+              '()))
+
 (defun seq-group-by (function seq)
   "Apply FUNCTION to each element of SEQ.
 Separate the elements of SEQ into an alist using the results as
@@ -318,6 +338,11 @@ This is an optimization for lists in `seq-take-while'."
       (setq n (+ 1 n)))
     n))
 
+(defun seq--activate-font-lock-keywords ()
+  "Activate font-lock keywords for some symbols defined in seq."
+  (font-lock-add-keywords 'emacs-lisp-mode
+                          '("\\<seq-doseq\\>")))
+
 (defalias 'seq-copy #'copy-sequence)
 (defalias 'seq-elt #'elt)
 (defalias 'seq-length #'length)
@@ -325,5 +350,7 @@ This is an optimization for lists in `seq-take-while'."
 (defalias 'seq-each #'seq-do)
 (defalias 'seq-map #'mapcar)
 
+(add-to-list 'emacs-lisp-mode-hook #'seq--activate-font-lock-keywords)
+
 (provide 'seq)
 ;;; seq.el ends here