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TorgoX (1933)

TorgoX
  sburkeNO@SPAMcpan.org
http://search.cpan.org/~sburke/

"Il est beau comme la retractilité des serres des oiseaux rapaces [...] et surtout, comme la rencontre fortuite sur une table de dissection d'une machine à coudre et d'un parapluie !" -- Lautréamont

Journal of TorgoX (1933)

Tuesday February 07, 2006
05:27 AM

Emacs fun: toggle-narrow

[ #28604 ]
Dear Log,

I've always wanted narrowing in emacs to be something I could just toggle, but there seemed no particularly easy would I could implement that. But the other day I finally sat down and banged this out:

(global-set-key "\M-n" 'toggle-narrow)

(defun toggle-narrow (beg end)
  "If narrow, widen; if not narrowed, narrow!"
  (interactive "r") ; "r" for region
  (if (narrow-p)
    (progn (widen)
      (message "Un-narrowing."))
    (progn (narrow-to-region beg end)
       (message "Narrowing to c%s - c%s." beg end))))

(defun narrow-p ()
  "Whether narrow is in effect for the current buffer"

  (let (real-point-min real-point-max)
    (save-excursion (save-restriction
    (widen)
    (setq real-point-min (point-min)
            real-point-max (point-max))))
    (or
     (/= real-point-min (point-min))
     (/= real-point-max (point-max)))))

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  • I've seen the command in the manual but have never really used it. It sounds clever, but it's not something I ever felt I whish I could use.

    Can you give a few real-life (as in "actual") scenarios when it's useful to use narrow?

    /J

    • I think I typically use narrow for restricting the range of a search-and-replace.

      Example: I'm working on an HTML document and I want to paste in some Perl code or something. I type <pre>, paste the code, and </pre>, and then I realize I need to turn the &'s in the Perl code into &amp;'s. So I select the Perl code that I just pasted in, hit Narrow, use replace-string to change &'s to &amp;, and then hit Widen.