buffer-substring-filter

["Chong Yidong" <cyd@stupidchicken.com>]

This patch implements the kill filter following RMS' suggestions, as a
variant of buffer-substring. Is it OK?

*** emacs/lisp/simple.el~	Mon Mar 14 20:50:53 2005
--- emacs/lisp/simple.el	Mon Mar 14 20:53:37 2005
***************
*** 2215,2220 ****
--- 2215,2251 ----
    (reset-this-command-lengths)
    (restore-overriding-map))
  \f
+ (defvar buffer-substring-filters nil
+   "List of filter functions for `filter-buffer-substring'.
+ Each function must accept a single argument, a string, and return
+ a string.  The buffer substring is passed to the first function
+ in the list, and the return value of each function is passed to
+ the next.  The return value of the last function is used as the
+ return value of `filter-buffer-substring'.
+ 
+ If this variable is nil, no filtering is performed.")
+ 
+ (defun filter-buffer-substring (beg end &optional delete)
+   "Return the buffer substring between BEG and END, after filtering.
+ The buffer substring is passed through each of the filter
+ functions in `buffer-substring-filters', and the value from the
+ last filter function is returned.  If `buffer-substring-filters'
+ is nil, the buffer substring is returned unaltered.
+ 
+ If DELETE is non-nil, the text between BEG and END is deleted
+ from the buffer.
+ 
+ This function should be used instead of `buffer-substring' or
+ `delete-and-extract-region' when you want to allow filtering to
+ take place.  For example, major or minor modes can use
+ `buffer-substring-filters' to extract characters that are special
+ to a buffer, and should not be copied into other buffers."
+   (let ((string (if delete (delete-and-extract-region beg end)
+                   (buffer-substring beg end))))
+     (mapcar (lambda (filter) (setq string (funcall filter string)))
+             buffer-substring-filters)
+     string))
+ 
  ;;;; Window system cut and paste hooks.
  
  (defvar interprogram-cut-function nil
***************
*** 2391,2397 ****
  text.  See `insert-for-yank'."
    (interactive "r")
    (condition-case nil
!       (let ((string (delete-and-extract-region beg end)))
  	(when string			;STRING is nil if BEG = END
  	  ;; Add that string to the kill ring, one way or another.
  	  (if (eq last-command 'kill-region)
--- 2422,2428 ----
  text.  See `insert-for-yank'."
    (interactive "r")
    (condition-case nil
!       (let ((string (filter-buffer-substring beg end t)))
  	(when string			;STRING is nil if BEG = END
  	  ;; Add that string to the kill ring, one way or another.
  	  (if (eq last-command 'kill-region)
***************
*** 2427,2434 ****
  system cut and paste."
    (interactive "r")
    (if (eq last-command 'kill-region)
!       (kill-append (buffer-substring beg end) (< end beg))
!     (kill-new (buffer-substring beg end)))
    (if transient-mark-mode
        (setq deactivate-mark t))
    nil)
--- 2458,2465 ----
  system cut and paste."
    (interactive "r")
    (if (eq last-command 'kill-region)
!       (kill-append (filter-buffer-substring beg end) (< end beg))
!     (kill-new (filter-buffer-substring beg end)))
    (if transient-mark-mode
        (setq deactivate-mark t))
    nil)
*** emacs/lisp/register.el~	Mon Mar 14 20:45:35 2005
--- emacs/lisp/register.el	Mon Mar 14 20:46:25 2005
***************
*** 277,283 ****
  Called from program, takes four args: REGISTER, START, END and DELETE-FLAG.
  START and END are buffer positions indicating what to copy."
    (interactive "cCopy to register: \nr\nP")
!   (set-register register (buffer-substring start end))
    (if delete-flag (delete-region start end)))
  
  (defun append-to-register (register start end &optional delete-flag)
--- 277,283 ----
  Called from program, takes four args: REGISTER, START, END and DELETE-FLAG.
  START and END are buffer positions indicating what to copy."
    (interactive "cCopy to register: \nr\nP")
!   (set-register register (filter-buffer-substring start end))
    (if delete-flag (delete-region start end)))
  
  (defun append-to-register (register start end &optional delete-flag)
***************
*** 289,295 ****
    (or (stringp (get-register register))
        (error "Register does not contain text"))
    (set-register register (concat (get-register register)
! 			    (buffer-substring start end)))
    (if delete-flag (delete-region start end)))
  
  (defun prepend-to-register (register start end &optional delete-flag)
--- 289,295 ----
    (or (stringp (get-register register))
        (error "Register does not contain text"))
    (set-register register (concat (get-register register)
! 			    (filter-buffer-substring start end)))
    (if delete-flag (delete-region start end)))
  
  (defun prepend-to-register (register start end &optional delete-flag)
***************
*** 300,306 ****
    (interactive "cPrepend to register: \nr\nP")
    (or (stringp (get-register register))
        (error "Register does not contain text"))
!   (set-register register (concat (buffer-substring start end)
  			    (get-register register)))
    (if delete-flag (delete-region start end)))
  
--- 300,306 ----
    (interactive "cPrepend to register: \nr\nP")
    (or (stringp (get-register register))
        (error "Register does not contain text"))
!   (set-register register (concat (filter-buffer-substring start end)
  			    (get-register register)))
    (if delete-flag (delete-region start end)))