Interface of entity calculator which is responsible for calculation of specific types of expression.

You can find more information in comments below.

class IEntityCalculator
    {
    public:
        virtual ERROR_INFO getLastError() = 0; // Return last error information 
        virtual IOperatorCalculator *getOperatorCalculator() = 0; // Return assigned or default operator calculator 
    
        virtual bool setOperatorCalculator(IOperatorCalculator *value) = 0; // Set new operator calculator. Old one will be destroyed. If nullptr is passes, default one will be used 
    
        virtual bool Pre(ICalculator *calculator, CExpression *expression, CVariable *parent, CVariable *value) = 0; // Apply "pre" operators(like ++x, --x) 
        virtual bool Post(ICalculator *calculator, CExpression *expression, CVariable *parent, CVariable *value) = 0; // Apply "post" operators(like, x++, x--). Could be applied only on identifier expression 
        virtual CVariable *List(ICalculator *calculator, CExpression *expression, CVariable *parent) = 0; // Calculate expresson of type List 
        virtual CVariable *Procedure(ICalculator *calculator, CExpression *expression, CVariable *parent) = 0; // Calculate expresson of type Procedure 
        virtual CVariable *Subscript(ICalculator *calculator, CExpression *expression, CVariable *parent) = 0; // Calculate expresson of type Subscript 
        virtual CVariable *Value(ICalculator *calculator, CExpression *expression, CVariable *parent) = 0; // Calculate expresson of type Value 
        virtual CVariable *Complex(ICalculator *calculator, CExpression *expression, CVariable *parent) = 0; // Calculate expresson of type Complex 
        virtual CVariable *Range(ICalculator *calculator, CExpression *expression, CVariable *parent) = 0; // Calculate expresson of type Range 
        virtual CVariable *Array(ICalculator *calculator, CExpression *expression, CVariable *parent) = 0; // Calculate expresson of type Array 
    
        virtual void Release() = 0; // Delete itself 
    };