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copied!<p>You need to write your own <a href="http://en.wikipedia.org/wiki/Recursive_descent_parser" rel="nofollow noreferrer">Recursive Descent Parser</a> from your BNF/EBNF. I had to write my own recently and <a href="http://www.cis.upenn.edu/~matuszek/General/recursive-descent-parsing.html" rel="nofollow noreferrer">this page</a> was a lot of help. I'm not sure what you mean by "with just code". Do you mean you want to know how to write your own recursive parser?</p> <p>If you want to do that, you need to have your grammar in place first. Once you have your EBNF/BNF in place, the parser can be written quite easily from it.</p> <p>The first thing I did when I wrote my parser, was to read everything in and then tokenize the text. So I essentially ended up with an array of tokens that I treated as a stack. To reduce the verbosity/overhead of pulling a value off a stack and then pushing it back on if you don't require it, you can have a <code>peek</code> method that simply returns the top value on the stack without popping it.</p> <p><strong>UPDATE</strong></p> <p>Based on your comment, I had to write a recursive-descent parser in Javascript from scratch. You can take a look at the parser <a href="http://github.com/vivin/regula/blob/master/regula.js" rel="nofollow noreferrer">here</a>. Just search for the <code>constraints</code> function. I wrote my own <code>tokenize</code> function to tokenize the input as well. I also wrote another convenience function (<code>peek</code>, that I mentioned before). The parser parses according to the EBNF <a href="http://github.com/vivin/regula/blob/master/constraint-definition.ebnf" rel="nofollow noreferrer">here</a>.</p> <p>This took me a little while to figure out because it's been years since I wrote a parser (last time I wrote it was in school!), but trust me, once you get it, you <em>get</em> it. I hope my example gets your further along on your way. </p> <p><strong>ANOTHER UPDATE</strong></p> <p>I also realized that my example may not be what you want because you might be going towards using a shift-reduce parser. You mentioned that right now you are trying to write a tokenizer. In my case, I did write my own tokenizer in Javascript. It's probably not robust, but it was sufficient for my needs.</p> <pre><code> function tokenize(options) { var str = options.str; var delimiters = options.delimiters.split(""); var returnDelimiters = options.returnDelimiters || false; var returnEmptyTokens = options.returnEmptyTokens || false; var tokens = new Array(); var lastTokenIndex = 0; for(var i = 0; i < str.length; i++) { if(exists(delimiters, str[i])) { var token = str.substring(lastTokenIndex, i); if(token.length == 0) { if(returnEmptyTokens) { tokens.push(token); } } else { tokens.push(token); } if(returnDelimiters) { tokens.push(str[i]); } lastTokenIndex = i + 1; } } if(lastTokenIndex < str.length) { var token = str.substring(lastTokenIndex, str.length); token = token.replace(/^\s+/, "").replace(/\s+$/, ""); if(token.length == 0) { if(returnEmptyTokens) { tokens.push(token); } } else { tokens.push(token); } } return tokens; } </code></pre> <p>Based on your code, it looks like you are reading, tokenizing, and parsing at the same time - I'm assuming that's what a shift-reduce parser does? The flow for what I have is tokenize first to build the stack of tokens, and then send the tokens through the recursive-descent parser.</p>

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