add parser for concat

StgSharp.RegularAnalysis/TextRegex/RegexInterpreter.cs

@@ -44,7 +44,11 @@ namespace StgSharp.RegularAnalysis.TextRegex
         {
             RegexTokenReader reader = new RegexTokenReader(regex);
             TokenParser<RegexElementLabel, RegexElementLabel> lexer = reader.Pipe(() => new RegexTokenParser());
+
+            while (lexer.TryReadToken(out Token<RegexElementLabel> token)) { }
         }
 
+        private static void
+
     }
 }

StgSharp.RegularAnalysis/TextRegex/RegexTokenReader.cs

@@ -45,6 +45,13 @@ namespace StgSharp.RegularAnalysis.TextRegex
 
         public RegexTokenReader() { }
 
+        public RegexTokenReader(
+               string source
+        )
+        {
+            _source = source;
+        }
+
         public bool IsEmpty => string.IsNullOrEmpty(_source) || position >= _source.Length;
 
         public Token<RegexElementLabel> ReadToken()