AddExpression add1 = new AddExpression(expPlan, constant1, constant2) ;
CastExpression cast1 = new CastExpression(expPlan,constant3, createFS(DataType.DOUBLE)) ;
MultiplyExpression mul1 = new MultiplyExpression(expPlan, add1, cast1) ;
CompilationMessageCollector collector = new CompilationMessageCollector() ;
TypeCheckingExpVisitor expTypeChecker = new TypeCheckingExpVisitor(expPlan, collector, null);
expTypeChecker.visit();
printMessageCollector(collector) ;
//printTypeGraph(plan) ;
if (collector.hasError()) {
throw new Exception("Error during type checking") ;