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POCan you propose a more elegant way to 'tokenize' c# code for html formatting?
 

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  1. POCan you propose a more elegant way to 'tokenize' c# code for html formatting?
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    <p><em>(<a href="https://stackoverflow.com/questions/174418/can-you-improve-this-lines-of-code-algorithm-in-f">This question</a> about refactoring F# code got me one down vote, but also some interesting and useful answers. And 62 F# questions out of the 32,000+ on SO seems pitiful, so I'm going to take the risk of more disapproval!)</em></p> <p>I was trying to post a bit of code on a blogger blog yesterday, and turned to <a href="http://manoli.net/csharpformat/" rel="nofollow noreferrer">this site</a>, which I had found useful in the past. However, the blogger editor ate all the style declarations, so that turned out to be a dead end.</p> <p>So (like any hacker), I thought "how hard can it be?" and rolled my own in &lt;100 lines of F#.</p> <p>Here is the 'meat' of the code, which turns an input string into a list of 'tokens'. Note that these tokens aren't to be confused with the lexing/parsing-style tokens. I did look at those briefly, and though I hardly understood anything, I did understand that they would give me <em>only</em> tokens, whereas I want to keep my original string.</p> <p>The question is: is there a more elegant way of doing this? I don't like the n re-definitions of s required to remove each token string from the input string, but it's difficult to split the string into potential tokens in advance, because of things like comments, strings and the #region directive (which contains a non-word character).</p> <pre><code>//Types of tokens we are going to detect type Token = | Whitespace of string | Comment of string | Strng of string | Keyword of string | Text of string | EOF //turn a string into a list of recognised tokens let tokenize (s:String) = //this is the 'parser' - should we look at compiling the regexs in advance? let nexttoken (st:String) = match st with | st when Regex.IsMatch(st, "^\s+") -&gt; Whitespace(Regex.Match(st, "^\s+").Value) | st when Regex.IsMatch(st, "^//.*?\r?\n") -&gt; Comment(Regex.Match(st, "^//.*?\r?\n").Value) //this is double slash-style comments | st when Regex.IsMatch(st, "^/\*(.|[\r?\n])*?\*/") -&gt; Comment(Regex.Match(st, "^/\*(.|[\r?\n])*?\*/").Value) // /* */ style comments http://ostermiller.org/findcomment.html | st when Regex.IsMatch(st, @"^""([^""\\]|\\.|"""")*""") -&gt; Strng(Regex.Match(st, @"^""([^""\\]|\\.|"""")*""").Value) // unescaped = "([^"\\]|\\.|"")*" http://wordaligned.org/articles/string-literals-and-regular-expressions | st when Regex.IsMatch(st, "^#(end)?region") -&gt; Keyword(Regex.Match(st, "^#(end)?region").Value) | st when st &lt;&gt; "" -&gt; match Regex.Match(st, @"^[^""\s]*").Value with //all text until next whitespace or quote (this may be wrong) | x when iskeyword x -&gt; Keyword(x) //iskeyword uses Microsoft.CSharp.CSharpCodeProvider.IsValidIdentifier - a bit fragile... | x -&gt; Text(x) | _ -&gt; EOF //tail-recursive use of next token to transform string into token list let tokeneater s = let rec loop s acc = let t = nexttoken s match t with | EOF -&gt; List.rev acc //return accumulator (have to reverse it because built backwards with tail recursion) | Whitespace(x) | Comment(x) | Keyword(x) | Text(x) | Strng(x) -&gt; loop (s.Remove(0, x.Length)) (t::acc) //tail recursive loop s [] tokeneater s </code></pre> <p>(If anyone is really interested, I am happy to post the rest of the code)</p> <p><strong>EDIT</strong> Using the <a href="https://stackoverflow.com/questions/228605/can-you-propose-a-more-elegant-way-to-tokenize-c-code-for-html-formatting/228609#228609">excellent suggestion</a> of <a href="http://blogs.msdn.com/chrsmith/archive/2008/02/21/Introduction-to-F_2300_-Active-Patterns.aspx" rel="nofollow noreferrer">active patterns</a> by kvb, the central bit looks like this, much better!</p> <pre><code>let nexttoken (st:String) = match st with | Matches "^\s+" s -&gt; Whitespace(s) | Matches "^//.*?\r?(\n|$)" s -&gt; Comment(s) //this is double slash-style comments | Matches "^/\*(.|[\r?\n])*?\*/" s -&gt; Comment(s) // /* */ style comments http://ostermiller.org/findcomment.html | Matches @"^@?""([^""\\]|\\.|"""")*""" s -&gt; Strng(s) // unescaped regexp = ^@?"([^"\\]|\\.|"")*" http://wordaligned.org/articles/string-literals-and-regular-expressions | Matches "^#(end)?region" s -&gt; Keyword(s) | Matches @"^[^""\s]+" s -&gt; //all text until next whitespace or quote (this may be wrong) match s with | IsKeyword x -&gt; Keyword(s) | _ -&gt; Text(s) | _ -&gt; EOF </code></pre>
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