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    <p>I would highly recommend the F# language as your language of choice for parsing on the .NET Platform. It's roots in the ML family of languages means it has excellent support for language-oriented programming.</p> <p>Discriminated unions and pattern-matching allow for a very succinct and powerful specification of your AST. Higher-order functions allow for definition of parse operations and their composition. First-class support for monadic types allows for state management to be handled implicitly greatly simplifying the composition of parsers. Powerful type-inference greatly aides the definition of these (complex) types. And all of this can be specified and executed interactively allowing you to rapidly prototype.</p> <p>Stephan Tolksdorf has put this into practice with his parser combinator library <a href="http://www.quanttec.com/fparsec/" rel="noreferrer">FParsec</a></p> <p>From his examples we see how naturally an AST is specified:</p> <pre><code>type expr = | Val of string | Int of int | Float of float | Decr of expr type stmt = | Assign of string * expr | While of expr * stmt | Seq of stmt list | IfThen of expr * stmt | IfThenElse of expr * stmt * stmt | Print of expr type prog = Prog of stmt list </code></pre> <p>the implementation of the parser (partially elided) is just as succinct:</p> <pre><code>let stmt, stmtRef = createParserForwardedToRef() let stmtList = sepBy1 stmt (ch ';') let assign = pipe2 id (str ":=" &gt;&gt;. expr) (fun id e -&gt; Assign(id, e)) let print = str "print" &gt;&gt;. expr |&gt;&gt; Print let pwhile = pipe2 (str "while" &gt;&gt;. expr) (str "do" &gt;&gt;. stmt) (fun e s -&gt; While(e, s)) let seq = str "begin" &gt;&gt;. stmtList .&gt;&gt; str "end" |&gt;&gt; Seq let ifthen = pipe3 (str "if" &gt;&gt;. expr) (str "then" &gt;&gt;. stmt) (opt (str "else" &gt;&gt;. stmt)) (fun e s1 optS2 -&gt; match optS2 with | None -&gt; IfThen(e, s1) | Some s2 -&gt; IfThenElse(e, s1, s2)) do stmtRef:= choice [ifthen; pwhile; seq; print; assign] let prog = ws &gt;&gt;. stmtList .&gt;&gt; eof |&gt;&gt; Prog </code></pre> <p>On the second line, as an example, <code>stmt</code> and <code>ch</code> are parsers and <code>sepBy1</code> is a monadic parser combinator that takes two simple parsers and returns a combination parser. In this case <code>sepBy1 p sep</code> returns a parser that parses one or more occurrences of <code>p</code> separated by <code>sep</code>. You can thus see how quickly a powerful parser can be combined from simple parsers. F#'s support for overridden operators also allow for concise infix notation e.g. the sequencing combinator and the choice combinator can be specified as <code>&gt;&gt;.</code> and <code>&lt;|&gt;</code>.</p> <p>Best of luck,</p> <p>Danny</p>
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