[PD] Fwd: Bug entering '{' characters WAS: who is using [entry]?

[Tim Blechmann]

On Sun, 2007-11-18 at 12:35 -0500, Hans-Christoph Steiner wrote:
> On Nov 18, 2007, at 4:56 AM, Claude Heiland-Allen wrote:
> 
> > Hans-Christoph Steiner wrote:
> >> So... anyone want to write a regexp that escapes any unclosed   
> >> brackets?  That would be a tricky one... but very useful for Pd.
> >
> > I guess that it's not possible at all with regular expressions:
> >
> > http://en.wikipedia.org/wiki/ 
> > Regular_language#Regular_languages_over_an_alphabet
> > --8<--
> > A simple example of a language that is not regular is the set of  
> > strings
> > { a^n b^n | n >= 0 }.
> > --8<--
> >
> > This is precisely the "matching brackets" problem.
> 
> regexps plus something else perhaps.  It's pretty simple to do, just  
> count open brackets and close brackets, see if there is a difference,  
> then go find the extra and escape it.  Many text editors keep track  
> of this stuff on the fly.

the language { a^n b^n | n >= 0 } cannot be described by a regular
expression, as it is not a regular language (easy to prove via the
pumping lemma). you need a parser for a context-free grammar in order to
match this structure ...

hth, tim

--
tim at klingt.org
http://tim.klingt.org

Most of the trouble in this world has been caused by folks who can't
mind their own business, because they have no business of their own to
mind, any more than a smallpox virus has.
  William S. Burroughs
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part
URL: <http://lists.puredata.info/pipermail/pd-list/attachments/20071118/54179c21/attachment.pgp>