Add support for ParNode in SyntaxNodeVisitor

com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/RSyntaxNodeVisitor.java

@@ -26,6 +26,10 @@ public interface RSyntaxNodeVisitor<T> extends IRSyntaxNodeVisitor<T> {
 
     public abstract T visit(final ReadVariableNode var);
 
+    public default T visit(final ParNode par) {
+        return par.getSyntaxArguments()[0].accept(this);
+    }
+
     public abstract T visit(final WriteLocalFrameVariableNode var);
 
     public abstract T visit(final FunctionExpressionNode fun);
@@ -70,6 +74,8 @@ public interface RSyntaxNodeVisitor<T> extends IRSyntaxNodeVisitor<T> {
             return visit((BlockNode) node);
         if (node instanceof ReadVariableNode)
             return visit((ReadVariableNode) node);
+        if (node instanceof ParNode)
+            return visit((ParNode) node);
         if (node instanceof WriteLocalFrameVariableNode)
             return visit((WriteLocalFrameVariableNode) node);
         if (node instanceof FunctionExpressionNode)