New function seq-position

* lisp/emacs-lisp/seq.el (seq-position): New function.
* test/automated/seq-tests.el: New tests for seq-position.
* doc/lispref/sequences.texi: Add documentation for `seq-position'.

1 files changed, 13 insertions, 2 deletions

diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
index ce6645a099a..f5189c7dc97 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: 2.0
+;; Version: 2.1
 ;; Package: seq
 
 ;; Maintainer: emacs-devel@gnu.org
@@ -294,12 +294,23 @@ found or not."
     count))
 
 (cl-defgeneric seq-contains (seq elt &optional testfn)
-  "Return the first element in SEQ that equals to ELT.
+  "Return the first element in SEQ that is equal to ELT.
 Equality is defined by TESTFN if non-nil or by `equal' if nil."
   (seq-some (lambda (e)
               (funcall (or testfn #'equal) elt e))
             seq))
 
+(cl-defgeneric seq-position (seq elt &optional testfn)
+  "Return the index of the first element in SEQ that is equal to ELT.
+Equality is defined by TESTFN if non-nil or by `equal' if nil."
+  (let ((index 0))
+    (catch 'seq--break
+      (seq-doseq (e seq)
+        (when (funcall (or testfn #'equal) e elt)
+          (throw 'seq--break index))
+        (setq index (1+ index)))
+      nil)))
+
 (cl-defgeneric seq-uniq (seq &optional testfn)
   "Return a list of the elements of SEQ with duplicates removed.
 TESTFN is used to compare elements, or `equal' if TESTFN is nil."