Emacs Lisp Regular Expression Match everything until character sequence

Question

I am trying to write a regular expression in emacs lisp that will match multi line comments.

For example:

{-
  Some

  Comment

  Here
-}

Should match as a comment. Basically, anything between {- and -}. I am able to almost do it by doing the following:

"\{\-[^-]*\-\}"

However, this will fail if the comment includes a - not immediately followed by }

So, it will not match correctly in this case:

{-
  Some -
  Comment -
  Here -
-}

Which should be valid.

Basically, I would like to match on everything (including newlines) up to the sequence -}

Thanks in advance!

If you submit that as a solution, I will award it to you. Otherwise, I will add it myself. — Joe
– Joe, Commented Dec 21, 2013 at 5:03
On additional consideration, this solution still does not work for some more complex comments. — Joe
– Joe, Commented Dec 21, 2013 at 13:32
If you still haven't resolved it, update you post with an example of what it didn't match. — Carl Groner
– Carl Groner, Commented Dec 22, 2013 at 0:45

Drew · Accepted Answer · 2013-12-21 16:52:11Z

1

Doesn't this work for you? {-[^-]*[^}]*-}

(You didn't specify things precisely, so I'm just guessing what you want. Must the {- and -} be at the line beginning? Must they be on lines by themselves? Must there be some other characters between them? Etc. For example, should it match a line like this? {--}?)

answered Dec 21, 2013 at 16:52

Drew

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Comments

Andreas Röhler · Accepted Answer · 2013-12-21 08:25:43Z

1

Made a toolkit for such cases. It comes with a parser, beg-end.el.

Remains to write a function, which will determine the beginning resp. the end of the object.

In pseudo-code:

(put 'MY-FORM 'beginning-op-at
           (lambda () (search-forward "-}")))

(put 'MY-FORM 'end-op-at
     (lambda () (search-backward "{-")))

When done, it's should be available, i.e. copied and returned like this

(defun MY-FORM-atpt (&optional arg)
  " "
  (interactive "p")
  (ar-th 'MY-FORM arg))

Get it here:

https://launchpad.net/s-x-emacs-werkstatt/

answered Dec 21, 2013 at 8:25

Andreas Röhler

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2 Comments

Joe Over a year ago

Does this return a regular expression? I am trying to use this with font-lock highlighting so it must be in the form of a regular expression.

Andreas Röhler Over a year ago

@Joe Example shown returns the string matched. Emacs-Werkstatt delivers related functions, which deliver beg-end positions etc. When searching a form defined by beginning and end, which spans an arbitrary number of lines, reg-exps can't match that reliably. A parser is needed. MY-FORM-atpt would call the parser on MY-FORM, reading the definitions. BTW the real case would ask if already at beginning, i.e. looking at "{-" - the lambda must be extended still. Also you will ask if it should match inside a string. Basically it should be useable to fontify any section found.

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