Re: elisp regexp, what does this mean?

[Alan Mackenzie]

heinz.eriksson@gmail.com wrote:
> I am trying to understand what the following:

> (defun erl-ie-eval-expression (node)
>  (interactive (list (erl-ie-read-nodename)))
>  (erl-ie-read-nodename)
>  (let ((end (point))
>        (beg (save-excursion
>               (loop do (re-search-backward "\\(\\`\\|^\\<\\)")
>                     while (looking-at "end"))
>               (point))))
>    (erl-ie-evaluate beg end node t)))

> Or rather the inner part involving the (scattered toothpick style)
> regexp.

OK, for a start, double backslashes are really just single ones - you
need to write them double because they're in a lisp string.  If you
write it out with this substitution, and on two lines, it looks like
this:

    \(  \|   \)
      \`  ^\<

This regexp matches EITHER a match for \` OR a match for ^\<.
\` matches anything at the beginning of the (visible part of the) buffer.
^\< matches the beginning of a word at the start of a line.

This is all documented on the page "Syntax of Regexps" in the Elisp
manual.

> BR

-- 
Alan Mackenzie (Nuremberg, Germany).