follow mode for occur

[Stephen Eglen <stephen@anc.ed.ac.uk>]

 > 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. 
 > 
A few years ago, I too wrote a "follow mode" based on the reftex
code.  You can get it from:
 http://www.anc.ed.ac.uk/~stephen/emacs/fm.el

Best wishes,
Stephen
[relevant doc appended below]

;;; Commentary:

;; As you move through the lines of an output buffer (such as from
;; `grep' or `occur'), another window highlights the corresponding
;; line of the source buffer.

;; This is inspired by the table of contents code from reftex.el.
;; http://www.strw.leidenuniv.nl/~dominik/Tools/

;;; Installation
;; To use the mode, do M-x fm-start in the output buffer.  Or just add
;; it to the mode hooks, e.g.:
;; (add-hook 'occur-mode-hook 'fm-start)
;; (add-hook 'compilation-mode-hook 'fm-start)
;; 

;;; Examples:
;;  
;; Do an occur for the word `package' in the NEWS file:
;; C-h n
;; M-x occur RTN package RTN

;; or test it on the current file:
;; (grep "grep -n 'def' fm.el")
;; (occur "def")

;; Once following is activated in a buffer, it can be toggled with the
;; "f" key in that buffer.

;; To extend this code to handle other types of output buffer, you
;; need to add an entry to the alist `fm-modes'.

;; If you want to use fm in a buffer that doesn't have a useful major
;; mode, you can always set the value of fm-defun yourself.  For
;; example, the cscope buffer is in fundamental mode, so in this case
;; we set fm-defun as a local variable to be the defun to use for
;; visiting the corresponding line of the source buffer.

(add-hook 'cscope-query-hook 'cscope-run-fm)

(defun cscope-run-fm ()
  "Run cscope in the fm buffer."
  (set (make-local-variable 'fm-defun) '(cscope-interpret-output-line))
  (fm-start))

;; If you are using this in the compile mode, you may find it easier
;; to use the key M-p to go to the previous error.  Otherwise, you may
;; find that if you go up one line, and this line doesn't have an
;; error on it, it goes down one line again, taking you back where you
;; started!