virtual void visit(ProgramSyntax::VariableReference &);
virtual void visit(ProgramSyntax::UnaryExpression &);
virtual void visit(ProgramSyntax::BinaryExpression &);
virtual void visit(ProgramSyntax::VariableReference &);
virtual void visit(ProgramSyntax::UnaryExpression &);
virtual void visit(ProgramSyntax::BinaryExpression &);