follow mode for occur

[Dan Nicolaescu]

The code below implements a follow mode for the *Occur*, this was
inspired by `reftex-toc-follow-mode'. 
Pointer motion in the *Occur* buffer determines motion in the
original buffer. This allows one to quickly browse the *Occur*
buffer while seeing the corresponding matches in the original buffer. 

To try this out just evaluate the elisp code below. 
C-c C-f toggles the follow mode. 

Is there an interest to have something like this included in Emacs? 
If there is I can provide a patch acceptable for inclusion. 

How about implementing something similar for compile.el? 
I can provide code for that too. 

Please let me know what do you think about this. 

Thanks.

        --dan


(defcustom occur-follow-mode t
  "*Non-nil means that poing motion in the Occur buffer causes the file to 
follow.")

;;; Internal variable for `occur-mode-post-command-hook'.
(defvar occur-follow-last-line nil)

;;; Used as a post-command-hook for the *Occur* buffer.
(defun occur-mode-post-command-hook ()
  (when occur-follow-mode
    (unless (equal occur-follow-last-line (line-number-at-pos))
      (setq occur-follow-last-line (line-number-at-pos))
      (condition-case nil
          (occur-mode-display-occurrence)
        (error t)))))

(add-hook 'occur-mode-hook 
          (lambda ()   
            (add-hook 'post-command-hook 'occur-mode-post-command-hook)))

(defun toggle-occur-follow-mode ()
  (interactive)
  (setq occur-follow-mode (not occur-follow-mode)))

(define-key occur-mode-map "\C-c\C-f" 'toggle-occur-follow-mode)