// SyntaxTree.java

// SyntaxTree is a class to represent a node of a binary syntax tree.

class SyntaxTree {

  private Object node;
  private SyntaxTree left;
  private SyntaxTree right;

  // constructor functions

  public SyntaxTree () { 
    this (null, null, null);
  }

  public SyntaxTree (Object nodeValue) {
    this (nodeValue, null, null);
  }

  public SyntaxTree (Object nodeValue, SyntaxTree leftTree) {
    this (nodeValue, leftTree, null);
  }

  public SyntaxTree (Object nodeValue, SyntaxTree leftTree, 
      SyntaxTree rightTree) {
    node  = nodeValue;
    left  = leftTree;
    right = rightTree;
  }

  // selector functions

  public String root ()      { return node . toString (); }
  public SyntaxTree left ()  { return left; }
  public SyntaxTree right () { return right; }
  public int constValue () { return ((Integer) left () . node) . intValue (); }
  public Location varLoc () { return (Location) left () . left () . node; }
  public SyntaxTree procBody() { return left () . left () . left (); }

  // print prints the tree in Cambridge Polish prefix notation with a heading.

  public void print (String block_name) {
    System . out . println ("");
    System . out . println ("Syntax Tree for " + block_name);
    System . out . print ("----------------");
    for (int i = 0; i < block_name . length (); i++)
      System . out . print ("-");
    System . out . println ("");
    System . out . println (this);
  }

  // toString returns the tree in Cambridge Polish prefix notation.

  public String toString () {
    if (root () . equals ("id"))
      return left () . root (); // return only id name
    else if (root () . equals ("int"))
      if (left () . left () == null) // integer constant
        return left () . root ();
      else                           // constant identifier
        return left () . left () . root ();
    if (left == null) 
      return root ();
    else if (right == null)
      return "(" + root () + " " + left + ")";
    else
      return "(" + root () + " " + left + " " + right + ")";
  }

}