/*  In this example of the visitor pattern, there are (initially) three
    kinds of visitees: grad student, undergrad student, and since the
    students are to exist in a collection, a default "no student", which
    plays the role of the algebraic identity (rational form of null).

    The modifier "internal" means that the item is visible (public) to all
    parts of the program that are compiled together.
*/

namespace visitorpatternexp
{ //////////////////////

using System;

public interface student        // abstract visitee
{
   object accept(svisitor v);
}

public interface svisitor       // abstract visitor
{
   object visitu(undergrad u);
   object visitg(grad g);
   object visitn(nostudent n);
}


// super class for what all students (visitees) have in common:
public class basicstudent
{
    internal string name;      // name of student
    internal double gpa;       // gpa of student
    internal double tuition;   // cost of tuition for student
    internal student next;     // pointer to next student (forms linked list)

    public basicstudent(string n, double g)   // constructor
    {   name = n; gpa = g;  
    }
} // basicstudent

// Concrete visitee classes

public class undergrad : basicstudent, student
{
   internal string major;  // undergrads have a major
   public undergrad(string n, double g, string m) : base(n,g)
   { major = m;  tuition = 600;  // per credit
   }
   public object accept(svisitor v) { return v.visitu(this); }

}//undergrad

public class grad : basicstudent, student
{
   internal string thesis;   // grads have a thesis topic
   public grad(string n, double g, string t) : base(n,g)
   {  thesis=t;  tuition = 700; }
   public object accept(svisitor v) { return v.visitg(this); }
}//grad

public class nostudent : student
{
   public object accept(svisitor v) { return v.visitn(this); }
}


}//////////////////////