Add comma to interpreter

src/interpreter.cpp

@@ -46,6 +46,7 @@ EvalResult eval(Node &ast, Memory &memory) {
     if (holds_alternative<InnerNode>(ast)) {
         InnerNode node = get<InnerNode>(ast);
         switch (node.type) {
+            case NodeType::Comma:
             case NodeType::Prog:
                 eval(node.children[0], memory);
                 return eval(node.children[1], memory);