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    <p>Well, you are using the wrong tool for the job (assuming you are also looking for nested scopes)</p> <p>Note that regex (in the traditional form of regex) stands for Regular Expression - which is a way to describe a <a href="http://en.wikipedia.org/wiki/Regular_language" rel="nofollow">Regular Language</a>.</p> <p>However, the language <code>L = { all words with legal scopings }</code> is irregular - and thus cannot be identified by regex.</p> <p>This langauge is actually <a href="http://en.wikipedia.org/wiki/Context-free_language" rel="nofollow">Conext Free Langauge</a>, and can be represented by a <a href="http://en.wikipedia.org/wiki/Context-free_grammar" rel="nofollow">Context Free Grammer</a>.</p> <p>For parsing: <br>For relatively simple langauges (scoping is among them) - a deterministic <a href="http://en.wikipedia.org/wiki/Pushdown_automaton" rel="nofollow">push-down automaton</a> is enough to verify them.</p> <p>Some languages require non deterministic push down automaton - which is not very efficiently created, but there is a <a href="http://en.wikipedia.org/wiki/CYK_algorithm" rel="nofollow">dynamic programming algorithm</a> to parse them as well.</p> <hr> <p>As a side note, there are some tools such as <a href="http://www.google.co.il/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;source=web&amp;cd=1&amp;ved=0CDYQFjAA&amp;url=http://javacc.java.net/&amp;ei=Yq1iUubUGqqk4gSY0IDABg&amp;usg=AFQjCNFvozNJ_Rxewupu63AzhtcPSHJu5A&amp;sig2=HCqX8AkfU3h4mGPIXA5adQ&amp;bvm=bv.54934254,d.bGE" rel="nofollow">JavaCC</a> that you can use to parse (and generate code/output) - have a look on them, but if you are simply looking for the scoping issue - it is probably an overkill.</p> <hr> <p>Edit - pseudo code:</p> <pre><code>curr &lt;- 0 count &lt;- 0 //integer imitates the stack for this simple usage l &lt;- string.length() while (curr &lt; l): if string.charAt(curr) == '{': count++; else if string.charAt(curr) == '}': if curr &lt;= 0: return ERROR; count--; curr++; if count != 0: return ERROR; return SUCCESS; </code></pre> <p>Note that in here we can use an integer to imitate the stack, in here an increase is basically a push() and a decrease is a pop().</p>
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    1. COHe's using the `layers` variable as a counter to simulate a stack in a PDA, so his approach would work just fine, assuming all braces have to be matched (e.g. they can't pop up unmatched in string literals or something).
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    2. CO@DaoWen don't you agree pushdown automaton will be more efficient, elegant and simple then repeatidly using a regex?
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    3. CONo, I don't see any real difference. PDAs are just NFAs with a stack added, and since NFAs and regexs are equivalent, adding the stack to the regex should be the exact same thing.
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