This is an abstract class that models a query expression. 
 
A class that models a Literal for a integer value. 
 
A class that models a Function expression. 
 
A static class with global function name definitions. 
 
Function & operator=(const Function &rhs)
 
virtual Expression * clone() const =0
It creates a new copy of this expression. 
 
std::vector< Expression * > m_args
The list of arguments. 
 
A static class with global function name definitions.