Display console in Emacs

When editing source, let it be source code or Tex source, we usually need another session for interactive operations like shell, REPL, compile log, etc.

I want the interactive session to be associated with the source and can easily switch on and off. The result is two function: toggle-console-buffer and toggle-console-window.

I primarily work on my laptop with only one window displayed. So normally I just switch between source buffer and the console buffer (the interactive session) by toggle-console-buffer. In other time, I want to see the update in console buffer while working in source buffer. toggle-console-window switches on a dedicated window¹ on the bottom. The clever thing is, when this window is live, toggle-console-buffer doesn’t switch to console buffer in the main window, but jumps to the console window at the bottom.

Here is the code:

(defvar luna-console-buffer-alist '((emacs-lisp-mode . "*scratch*"))
  "An alist with element (major-mode . console buffer).")

(defvar-local luna-console-buffer-p nil
  "T if this buffer is a console buffer.")

(defun luna--get-console-buffer (major-mode)
  "Return the console buffer corresponding to MAJOR-MODE.
Return nil if none exists."
  (if-let ((console-buffer (alist-get major-mode luna-console-buffer-alist)))
      console-buffer
    (message "No console buffer, use `luna-set-console-buffer' to set one")
    nil))

(defun luna-toggle-console ()
  "Toggle display of console buffer.
When console window is live, jump between console window and previous window;
when console window is not live, switch between console buffer and previous buffer."
  (interactive)
  (if (window-live-p luna-console-window)
      ;; jump between console window and previous window
      (if luna-console-buffer-p
          (if-let ((win (window-parameter luna-console-window 'luna-console-jump-back)))
              (select-window win)
            (select-window (previous-window))
            (message "Could not find previous window, guess one"))
        (let ((old-window (selected-window)))
          (select-window luna-console-window)
          (set-window-parameter nil 'luna-console-jump-back old-window)))
    ;; switch between console buffer and previous buffer
    (if luna-console-buffer-p
        (previous-buffer)
      (switch-to-buffer (luna--get-console-buffer major-mode))
      (setq-local luna-console-buffer-p t))))

(defun luna-set-console-buffer (buffer)
  "Set current console buffer to BUFFER."
  (interactive "b")
  (setf (alist-get major-mode luna-console-buffer-alist)
        (get-buffer buffer)))

(defvar luna-console-window nil
  "A window at bottom dedicated to console buffer.")

(defun luna-toggle-console-window ()
  "Toggle display of console window."
  (interactive)
  (if (window-live-p luna-console-window)
      (delete-window luna-console-window)
    (when-let ((buf (luna--get-console-buffer major-mode)))
      (setq luna-console-window
            (display-buffer-at-bottom (get-buffer buf) '((window-height . 0.2)))))))

Some note:

I associate the major mode of source to a single console buffer (or the buffer name). Add new associations by pushing new key-value pair to the alist:

(add-to-list 'luna-console-buffer-alist '(haskell-mode . "*haskell*"))

I never use multiple frames so the above code needs adjustment to work with that. For example, luna-console-window should probably be a frame parameter.

Footnotes:

I didn’t use set-window-dedicated-p so it’s not really dedicated.