// step 2
// the way step 1 built the tree was not quite satisfactory,
// it would be very easy to get all those pointers mixed up,
// and programming from the bottom up is always confusing.
//
// now we make a nice top-down construction

#include <iostream>
#include <string>
#include <vector>

struct node
{ string kind, detail;
  vector <node *> ptr;

  node(string a, string b="")
  { kind=a;
    detail=b; }

  node * add(node * p)
  { ptr.push_back(p);
    return this; }

  void print()
  { cout << "[" << kind << "," << detail;
    for (int i=0; i<ptr.size(); i+=1)
    { cout << ",";
      ptr[i]->print(); }
    cout << "]"; }
};

node * nn(string a, string b="")
{ return new node(a, b); }

void main()
{ node * p = nn("assign")
               ->add(nn("variable", "y"))
               ->add(nn("operation", "*")
                       ->add(nn("variable", "y"))
                       ->add(nn("number", "2")));
  p->print();
  cout << "\n"; }