I'm trying to write some buffer switching function (which in itself may be a fool's errand, but I digress...) - and it looks a little like this

(defun swk--quit-buffer (original-buffer)
  (switch-to-buffer (original-buffer))
  (kill-buffer "*tmp*")
  (local-unset-key "q"))

(defun swk-switcheroo ()
  (let ((temp-buf-name "*tmp*")
        (current-buffer-name (buffer-name)))
    (get-buffer-create temp-buf-name)
    (switch-to-buffer temp-buf-name)
    (local-set-key "q" (lambda ()
                         (swk--quit-buffer current-buffer-name)))))

My aim is to be able to temporarily bind "q" to this window, to simulate special-mode's "quittable" buffer. Sure enough, the "q" key works once, but I get the message:

Symbol's value as variable is void current-buffer-name

Ideally, I want to replace the current buffer with the result of invoking swk-switcheroo - and then reinstate the original buffer when the user presses "q".

1 Answer 1


You're tripping over dynamic binding (as opposed to lexical binding).

Your current-buffer-name is unbound at the point that your (lambda) function is executed. The let expression only binds it during the function's definition -- there's no closure to capture that value for subsequent evaluation.

One simple workaround is to use backquoting like so:

`(lambda ()
   (swk--quit-buffer ',current-buffer-name))
  • so how would I go about capturing that information? is this approach non-idiomatic? i've taken a look at save-excursion and display-buffer - perhaps they are better alternatives?
    – sunwukung
    Aug 2, 2015 at 22:10
  • @sunwukung Since Emacs 24, the idiomatic way would be to enable lexical binding. In earlier versions, phils' method is the best you can do. Aug 3, 2015 at 8:15

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