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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.io gmane.emacs.devel:274854 Archived-At: diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el index f0dc283f57d5..b7dcde87f412 100644 --- a/lisp/emacs-lisp/seq.el +++ b/lisp/emacs-lisp/seq.el @@ -467,6 +467,17 @@ seq-partition (setq sequence (seq-drop sequence n))) (nreverse result)))) +(cl-defgeneric seq-union (sequence1 sequence2 &optional testfn) + "Return a list of all elements that appear in either SEQUENCE1 or SEQUEN= CE2. +Equality is defined by TESTFN if non-nil or by `equal' if nil." + (let ((accum (lambda (acc elt) + (if (seq-contains-p acc elt testfn) + acc + (cons elt acc))))) + (seq-reverse + (seq-reduce accum sequence2 + (seq-reduce accum sequence1 '()))))) + `seq-reverse' seems gratuitous here WRT the purpose of `seq-union'. Given that this is a set operation, it makes more sense not to waste resources on element order. ( For comparison, both Common Lisp (n)union [1] and SRFI-1 lset-union [2] leave the element order unspecified, and e.g. in SBCL: * (union '(a b c) '(f a d)) (C B F A D) [1] http://www.lispworks.com/documentation/HyperSpec/Body/f_unionc.htm [2] https://srfi.schemers.org/srfi-1/srfi-1.html ) --=20 =C5=A0t=C4=9Bp=C3=A1n