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copied!<p>The Spark grammar is implemented with a kind-of-fluent domain specific language. </p> <p>It's declared in a few layers. The rules which recognize the html syntax are declared in <a href="http://github.com/loudej/spark/blob/master/src/Spark/Parser/Markup/MarkupGrammar.cs" rel="nofollow noreferrer">MarkupGrammar.cs</a> - those are based on grammar rules copied directly from the xml spec.</p> <p>The markup rules refer to a limited subset of csharp syntax rules declared in <a href="http://github.com/loudej/spark/blob/master/src/Spark/Parser/Code/CodeGrammar.cs" rel="nofollow noreferrer">CodeGrammar.cs</a> - those are a subset because Spark only needs to recognize enough csharp to adjust single-quotes around strings to double-quotes, match curley braces, etc.</p> <p>The individual rules themselves are of type <a href="http://github.com/loudej/spark/blob/master/src/Spark/Parser/ParseAction.cs" rel="nofollow noreferrer">ParseAction<TValue> delegate</a> which accept a <a href="http://github.com/loudej/spark/blob/master/src/Spark/Parser/Position.cs" rel="nofollow noreferrer">Position</a> and return a <a href="http://github.com/loudej/spark/blob/master/src/Spark/Parser/ParseResult.cs" rel="nofollow noreferrer">ParseResult</a>. The ParseResult is a simple class which contains the TValue data item parsed by the action and a new Position instance which has been advanced past the content which produced the TValue.</p> <p>That isn't very useful on it's own until you introduce a <a href="http://github.com/loudej/spark/blob/master/src/Spark/Parser/Position.cs" rel="nofollow noreferrer">small number of operators</a>, as described in <a href="http://en.wikipedia.org/wiki/Parsing_expression_grammar" rel="nofollow noreferrer">Parsing expression grammar</a>, which can combine single parse actions to build very detailed and robust expressions about the shape of different syntax constructs.</p> <p>The technique of using a delegate as a parse action came from a Luke H's blog post <a href="http://blogs.msdn.com/lukeh/archive/2007/08/19/monadic-parser-combinators-using-c-3-0.aspx" rel="nofollow noreferrer">Monadic Parser Combinators using C# 3.0</a>. I also wrote a post about <a href="http://whereslou.com/2008/05/15/creating-a-domain-specific-language-for-parsing" rel="nofollow noreferrer">Creating a Domain Specific Language for Parsing</a>.</p> <p>It's also entirely possible, if you like, to reference the Spark.dll assembly and inherit a class from the base CharGrammar to create an entirely new grammar for a particular syntax. It's probably the quickest way to start experimenting with this technique, and an example of that can be found in <a href="http://github.com/loudej/spark/blob/master/src/Spark.Tests/Parser/CharGrammarTester.cs" rel="nofollow noreferrer">CharGrammarTester.cs</a>.</p>

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