Re: about "forward-paragraph" in Intro to emacs lisp.

[Barry Margolin]

In article <mailman.3183.1248634897.2239.help-gnu-emacs@gnu.org>,
 waterloo <waterloo2005@gmail.com> wrote:

> I can not understand code of forward-paragraph in Intro to emacs lisp.
> 
> On " The forward motion `while' loop " of 12.4 in Intro to emacs lisp.
> -------------------------------
>      ;; going forwards and not at the end of the buffer
>      (while (and (> arg 0) (not (eobp)))
> 
>        ;; between paragraphs
>        ;; Move forward over separator lines...
>        (while (and (not (eobp))
>                    (progn (move-to-left-margin) (not (eobp)))
>                    (looking-at parsep))
>          (forward-line 1))
>        ;;  This decrements the loop
>        (unless (eobp) (setq arg (1- arg)))
>        ;; ... and one more line.
>        (forward-line 1)
> -----------------------------------------------------
> 
> Why need "(progn (move-to-left-margin) (not (eobp))) " ?

You only want 'and' to check the value of (not (eobp)), you don't want 
it looking at the value of (move-to-left-margin).  So you combine them 
with 'progn', which just returns the value of its last expression.

(move-to-left-margin) is needed because the parsep regexp is expected to 
be found at the beginning of line.

> Why need the last line " (forward-line 1) " ?

Not sure about that one.  I guess it wants to move to the beginning of 
the next paragraph, rather than the end of the current one.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
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