// the new value, and so that attributeChanged()
// is called on the actor.
parameter.validate();
} catch (IllegalActionException ex) {
ParseTreeFreeVariableCollector collector = new ParseTreeFreeVariableCollector();
Set expressionVariables = collector
.collectFreeVariables(parseTree);
Set scopeVariables = _scope.identifierSet();
List<String> excludedVariables = new LinkedList<String>();
for (Object variable : expressionVariables) {
if (variable instanceof String) {