解离出Runner

DoRunner/ExpressionRunner.cs

@@ -0,0 +1,14 @@
+using Convention.RScript.Parser;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Convention.RScript.Runner
+{
+    public class ExpressionRunner : IRSentenceRunner
+    {
+        [return: MaybeNull]
+        public object Run(ExpressionParser parser, RScriptSentence sentence, RScriptContext context)
+        {
+            return parser.Evaluate(sentence.content);
+        }
+    }
+}