[ruby-talk:18077] Re: Best way to prevent infinite loops...

> > 	Howdy.  What's the best way to prevent infinite loops in Ruby? =20
>=20
> Don't write one.  :)

	I wish I could...  I'm using a recursive regexp to remove all
<?tmpl.* ?> tags from a template and tags can include tags.

> I guess I'd ask: what's the driver of the loop? Is it the test for
> some_action, or is it the count, or both. If the count is incidental,
> then I'd tuck it away inside the loop (although possibly making it
> slightly shorter)

	In a nut shell, here's what I'm doing:

    tmpl =3D large_string
    tag_re =3D Regexp.new('\<\?tmpl\.([^\s\?]*)\s*(.*?)\s*\?\>')
    loop_count =3D 0
    while md =3D tag_re.match(tmpl)
      if loop_count > @max_num_iteration
        raise(RuntimeError, "Too many iterations")
      else
        loop_count +=3D 1
      end
      ...
      tag =3D md.to_a[0]
      ...
      tmpl.gsub!(/#{Regexp.escape(tag)}/, val)
      ...
    end

>   while some_action and loop_count < 1000

	I kinda like this, but want to raise an exception in the event
that it loops on for a while.  I think what I'll probably do is
reimplement this as a range and test for the Exception after I've
incremented over the range (that way I don't test whether to raise an
exception on every iteration).  Any thoughts are welcome.

<promoter>
	Actually, let me take this opportunity to put in a shameless
plug for the ruby-tmpl library that runs under mod_ruby.  I've just
released version 0.2 of this library and would love to get this out and
running on more systems.  The project is being hosted at SourceForge and
can be checked out at:

http://ruby-tmpl.sourceforge.net/

	A few tid bits about it:

1) It does work and is stable to use.  I eat my own dog food and am=20
developing two sites with it right now.

2) It is primarily used for creating dynamic/templated pages, however I
do anticipate having offline functionality completed by 0.3 so that
pages can be compiled offline.

3) This is not a replacement of eRuby, it's only a templating library
for sites that need to separate functionality/information from
presentation.  It is a module that works in parallel with mod_ruby.

4) There is an output filtering layer that I hope to expose and use
more.  Some of the things that I plan on doing real soon are add session
support (using both URIs and cookies) and dictionaries support
(keyword -> url mapping).

5) I'd like to think that things are well organized and documented,
please prove me wrong (or die trying).

	Please feel free to join the -users and -devel list. =20
Documentation about how/where is listed under the FAQs on the site. =20
Enjoy!  --Sean

http://ruby-tmpl.sourceforge.net/
</promoter>

--=20
Sean Chittenden