// step 1
// a structured program is like a big data structure. 
// A tree in fact
// when the copier works again, I'll scan a better picture for you.
// for now, here's a little ugly one
//
// y = y * 2   (a very little program indeed)
//   
//      +------------+
//----->|  "assign"  |
//      +------------+
//      |            |
//      +------------+            +------------+
//      |     @------+----------->| "variable" |
//      +------------+            +------------+
//      |     @------+------      |     "y"    |
//      +------------+     |      +------------+
//                         |
//                         |
//                         |      +-------------+
//                         ------>| "operation" |
//                                +-------------+
//                                |     "*"     |
//                                +-------------+          +------------+
//                                |      @------+--------->| "variable" |
//                                +-------------+          +------------+
//                                |      @------+-----     |     "y"    |
//                                +-------------+    |     +------------+
//                                                   |
//                                                   |
//                                                   |     +------------+
//                                                   ----->|  "number"  |
//                                                         +------------+
//                                                         |     "2"    |
//                                                         +------------+
//
//
// the nodes in the data structure that represents a program all have
// one string to say what kind of thing they represent, an optional
// second string to give more detail, and any number of pointers to
// other nodes.
//
// the little program below builds the tree for y=y*2

#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 * a = nn("variable", "y");
  node * b = nn("number", "2");
  node * c = nn("operation", "*")->add(a)->add(b);
  node * d = nn("variable", "y");
  node * e = nn("assign")->add(d)->add(c);
  e->print();
  cout << "\n"; }