From: Jimmy Thrasher <jjthrash@...>
Date: 2001-10-24T04:07:40+09:00
Subject: [ruby-talk:23072] Re: splitting a string with nested elements

At 03:53 AM 10/24/2001 +0900, you wrote:
>string = "start {{blah {{ }} outside\n{{ {{ }}\n}} bye"
>pre = Regexp.escape("{{")
>post = Regexp.escape("}}")
...
>which is close to what I want.  I really want:
>"start "
>"blah {{ "
>" outside\n"
>" {{ }}\n"
>" bye"
>
>Is there a way to do such a thing with a regex, or do I need to resort
>to a scanning technique, keeping track of the nested elements?

Joe,

Technically, what you want can't be done by a regular expression, since 
it's got nested elements (which are context-free, like Ruby, but not 
regular).  However, it should be pretty simple to do by tokenizing the 
string and keeping a stack, like so:

<untested code>
string = "start {{blah {{ }} outside\n{{ {{ }}\n}} bye"
pre = Regexp.escape("{{")
post = Regexp.escape("}}")
re = /(?:#{pre}|#{post})|(?:[^#{pre}|#{post}])/
string.scan(re) {
   | match |
   if match =~ /#{pre}|#{post}/
     # do some stack pushing and popping
   end
}
</untested code>

Jimmy