feat: Parser Combinator库和词法分析器 (#2)

Reviewed-on: https://git.bupt-hpc.cn/jackfiled/CanonSharp/pulls/2
Co-authored-by: jackfiled <xcrenchangjun@outlook.com>
Co-committed-by: jackfiled <xcrenchangjun@outlook.com>

CanonSharp.Combinator/Text/StringParser.cs

@@ -0,0 +1,22 @@
+using CanonSharp.Combinator.Abstractions;
+using CanonSharp.Combinator.Extensions;
+using CanonSharp.Combinator.Parsers;
+
+namespace CanonSharp.Combinator.Text;
+
+/// <summary>
+/// 字符串解析器
+/// </summary>
+/// <param name="except">期望的字符串</param>
+/// <param name="comparison">字符串比较模式</param>
+public class StringParser(string except, StringComparison comparison) : PrimitiveParser<char, string>
+{
+    protected override ParseResult<char, string> Run<TState>(TState state)
+    {
+        TState[] states = state.AsEnumerable<char, TState>().Take(except.Length).ToArray();
+        string actual = new(states.Select(x => x.Current).ToArray());
+        return string.Equals(except, actual, comparison)
+            ? ParseResultBuilder.Succeed<char, TState, string>(actual, states.Length == 0 ? state : states.Last().Next)
+            : ParseResultBuilder.Fail<char, TState, string>($"Except '{except}' but found '{actual}.", state);
+    }
+}