MultiRegexDemo.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace MultiRegex
{
	class Program
	{
		static void Main(string[] args)
		{
			var mr = new MultiRegex(new Dictionary<string, string>()
				{
					{ @"(\d+)", "number" },
					{ @"\b([a-zA-Z_][a-zA-Z0-9_]+)\b", "ident" },
					{ @";", "punct" },
				});

			var input = "76 trombones led the big parade;" +
				"With a 110 cornets close at hand ...";
			var toks = ParseWithMulti(mr, input);

			foreach( var t in toks )
				Console.WriteLine(t);
		}

		static IEnumerable<string> ParseWithMulti(MultiRegex mr, string input)
		{
			var index = 0;
			while( index < input.Length )
			{
				var m = mr.Match(input, index);
				if (m == null) yield break;

				yield return m.tag;
				index = m.m.Index + m.m.Length;
			}
		}
	}

	class MultiRegex
	{
		readonly Regex r;

		public MultiRegex(Dictionary<string, string> vs)
		{
			r = new Regex(vs
				.Select(v => "(?<{0}>{1})".F(v.Value, v.Key))
				.JoinWith("|"));
		}

		public MultiMatch Match(string s) { return Match(s, 0); }
		public MultiMatch Match(string s, int start)
		{
			var m = r.Match(s, start);
			if (!m.Success) return null;

			var namedGroups = r.GetGroupNames().Where(g => !char.IsDigit(g[0]));
			var tag = namedGroups
				.Select(x => new { t = x, g = m.Groups[x] })
				.Where(g => g.g.Success)
				.OrderBy(g => g.g.Index)
				.FirstOrDefault();

			if (tag == null) return null;
			return new MultiMatch(m, tag.t);
		}
	}

	class MultiMatch
	{
		public readonly Match m;
		public readonly string tag;

		public MultiMatch(Match m, string tag)
		{
			this.m = m;
			this.tag = tag;
		}
	}

	static class Exts
	{
		public static string F( this string f, params object[] args )
		{
			return string.Format( f, args );
		}

		public static string JoinWith<T>(this IEnumerable<T> ts, string sep)
		{
			return string.Join(sep, ts.Select(t => t.ToString()).ToArray());
		}
	}
}