toggle the line-length of an entire document?

[Sharon Kimble]

I'm currently using this to toggle line-length -

--8<---------------cut here---------------start------------->8---
(setq-default fill-column 100)
(defvar my-last-fill-col 75 "...")

(defun my-toggle-fill-column ()
   "..."
   (interactive)
   (setq-default my-last-fill-col
                 (prog1 fill-column
                   (setq-default fill-column my-last-fill-col)))
   (message "Fill column is now %d" fill-column))
--8<---------------cut here---------------end--------------->8---

Which works great for individual paragraphs, but now I want to toggle
the line-length of an entire document, but I can't work out how I'm
supposed to do it, so can anyone help please? Great aunt google hasn't
been much help so far! :)

Any ideas please folks?

Thanks
Sharon.
-- 
A taste of linux = http://www.sharons.org.uk
TGmeds = http://www.tgmeds.org.uk
Debian 8.4, fluxbox 1.3.7, emacs 25.1.1

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