(add-to-history): New function.

[gnu-emacs] / lisp / subr.el

diff --git a/lisp/subr.el b/lisp/subr.el
index 8b8416375b17afe081bcb3e116fd47451b0bd502..82d60a34d5f282e38e2f62c528c31217d01bf644 100644 (file)
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -1122,6 +1122,32 @@ The return value is the new value of LIST-VAR."
                            (if (and oa ob)
                                (< oa ob)
                              oa)))))))
+
+(defun add-to-history (history-var newelt &optional maxelt keep-dups)
+  "Add NEWELT to the history list stored in the variable HISTORY-VAR.
+Return the new history list.
+If MAXELT is non-nil, it specifies the maximum length of the history.
+Otherwise, the maximum history length is the value of the `history-length'
+property on symbol HISTORY-VAR, if set, or the value of the `history-length'
+variable.
+Remove duplicates of NEWELT unless `history-delete-duplicates' is nil
+or KEEP-DUPS is non-nil."
+  (unless maxelt
+    (setq maxelt (or (get history-var 'history-length)
+                    history-length)))
+  (let ((history (symbol-value history-var))
+       tail)
+    (if (and history-delete-duplicates (not keep-dups))
+       (setq history (delete newelt history)))
+    (setq history (cons newelt history))
+    (when (integerp maxelt)
+      (if (= 0 maxelt)
+         (setq history nil)
+       (setq tail (nthcdr (1- maxelt) history))
+       (when (consp tail)
+         (setcdr tail nil))))
+    (set history-var history)))
+
 \f
 ;;;; Mode hooks.