compat-31: New function ensure-proper-list

1 files changed, 12 insertions, 0 deletions

diff --git a/compat-31.el b/compat-31.el
index 4133bdb..0c1a228 100644
--- a/compat-31.el
+++ b/compat-31.el
@@ -29,6 +29,18 @@
 
 ;;;; Defined in subr.el
 
+(compat-defun ensure-proper-list (object) ;; <compat-tests:ensure-proper-list>
+  "Return OBJECT as a list.
+If OBJECT is already a proper list, return OBJECT itself.  If it's not a
+proper list, return a one-element list containing OBJECT.
+
+`ensure-list' is usually preferable because that function runs in
+constant time, but this one has to traverse the whole of OBJECT."
+  (declare (side-effect-free error-free))
+  (if (proper-list-p object)
+      object
+    (list object)))
+
 (compat-defun set-local (variable value) ;; <compat-tests:set-local>
   "Make VARIABLE buffer local and set it to VALUE."
   (set (make-local-variable variable) value))