First pass at a markdown parser in Dart.

utils/markdown/lib.dart

Index: utils/markdown/lib.dart
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+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Parses text in markdown format. Use this entrypoint if you want to parse
+/// markdown from your own Dart code. To parse markdown by running the script
+/// directly from the command line, see markdown.dart.
+#library('markdown');
+
+#source('ast.dart');
+#source('block_parser.dart');
+#source('html_renderer.dart');
+#source('inline_parser.dart');
+
+/// Converts the given string of markdown to HTML.
+String markdownToHtml(String markdown) {
+  final document = new Document();
+
+  final lines = markdown.split('\n');
+  document.parseRefLinks(lines);
+  final blocks = document.parseLines(lines);
+  return renderToHtml(blocks);
+}
+
+/// Replaces `<`, `&`, and `>`, with their HTML entity equivalents.
+String escapeHtml(String html) {
+  return html.replaceAll('&', '&amp;')
+             .replaceAll('<', '&lt;')
+             .replaceAll('>', '&gt;');
+}
+
+/// Maintains the context needed to parse a markdown document.
+class Document {
+  final Map<String, Link> refLinks;
+
+  Document()
+    : refLinks = <String, Link>{};
+
+  parseRefLinks(List<String> lines) {
+    /// This is a hideous regex. It matches:
+    /// [id]: http:foo.com "some title"
+    /// Where there may whitespace in there, and where the title may be in
+    /// single quotes, double quotes, or parentheses.
+    final indent = @'^[ ]{0,3}'; // Leading indentation.
+    final id = @'\[([^\]]+)\]';  // Reference id in [brackets].
+    final quote = @'"[^"]+"';    // Title in "double quotes".
+    final apos = @"'[^']+'";     // Title in 'single quotes'.
+    final paren = @"\([^)]+\)";  // Title in (parentheses).
+    final pattern = new RegExp(
+        '$indent$id:\\s+(\\S+)\\s*($quote|$apos|$paren|)\\s*\$');
+
+    for (int i = 0; i < lines.length; i++) {
+      final match = pattern.firstMatch(lines[i]);
+      if (match != null) {
+        // Parse the link.
+        final id = match.group(1);
+        final url = match.group(2);
+        var title = match.group(3);
+
+        if (title == '') {
+          // No title.
+          title = null;
+        } else {
+          // Remove "", '', or ().
+          title = title.substring(1, title.length - 1);
+        }
+
+        refLinks[id] = new Link(id, url, title);
+
+        // Remove it from the output. We replace it with a blank line which will
+        // get consumed by later processing.
+        lines[i] = '';
+      }
+    }
+  }
+
+  /// Parse the given [lines] of markdown to a series of AST nodes.
+  List<Node> parseLines(List<String> lines) {
+    final parser = new BlockParser(lines, this);
+
+    final blocks = [];
+    while (!parser.isDone) {
+      for (final syntax in BlockSyntax.syntaxes) {
+        if (syntax.canParse(parser)) {
+          final block = syntax.parse(parser);
+          if (block != null) blocks.add(block);
+          break;
+        }
+      }
+    }
+
+    return blocks;
+  }
+
+  /// Takes a string of raw text and processes all inline markdown tags,
+  /// returning a list of AST nodes. For example, given ``"*this **is** a*
+  /// `markdown`"``, returns:
+  /// `<em>this <strong>is</strong> a</em> <code>markdown</code>`.
+  List<Node> parseInline(String text) {
+    return new InlineParser(text, this).parse();
+  }
+}
+
+class Link {
+  final String id;
+  final String url;
+  final String title;
+  Link(this.id, this.url, this.title);
+}