Syntax highlighting from parser

.. oopsie on binary expression.

NOTE: it may be better to highlight tokens rather than
      via the parser as errors make it impossible to
      highlight the "intention" of the user

src/DataFilter.cpp

@@ -265,6 +265,7 @@ void Leaf::color(Leaf *leaf, QTextDocument *document)
     case Leaf::BinaryOperation : 
                     leaf->color(leaf->lvalue.l, document);
                     leaf->color(leaf->rvalue.l, document);
+                    return;
                     break;
 
     case Leaf::Function :