1 files changed, 12 insertions, 0 deletions
diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
index 300fe5cd1fd..8b7b594f5e1 100644
--- a/lisp/emacs-lisp/seq.el
+++ b/lisp/emacs-lisp/seq.el
@@ -144,6 +144,18 @@ if positive or too small if negative)."
             sequence)
     (nreverse result)))
 
+(defun seq-map-indexed (function sequence)
+  "Return the result of applying FUNCTION to each element of SEQUENCE.
+Unlike `seq-map', FUNCTION takes two arguments: the element of
+the sequence, and its index within the sequence."
+  (let ((index 0))
+    (seq-map (lambda (elt)
+               (prog1
+                   (funcall function elt index)
+                 (setq index (1+ index))))
+             sequence)))
+
+
 ;; faster implementation for sequences (sequencep)
 (cl-defmethod seq-map (function (sequence sequence))
   (mapcar function sequence))