/*	AST.java
	Abstract Syntax Tree implementation
*/

public class AST
{ private char node;		// holds node operator
  private Object val;		// holds node value
  private AST left, right;	// left and right subtrees

  // Constructor - construct AST leaf with integer value
  public AST(Object value)
  { node = '#';
    val = value;
  }

  // Constructor - construct AST node for operator with one operand
  public AST(char op, AST arg)
  { node = op;
    left = arg;
  }

  // Constructor - construct AST node for operator with two operands
  public AST(char op, AST arg1, AST arg2)
  { node = op;
    left = arg1;
    right = arg2;
  }

  // toLisp - Print AST as a Lisp expression
  public void toLisp()
  { switch (node)
    { case '#':		// leaf with integer constant
        System.out.print(" " + val);
        break;
      case '+':
      case '-':
      case '*':
      case '/':
        System.out.print(" (" + node);
        left.toLisp();
        right.toLisp();
        System.out.print(")");
        break;
      case '%':		// unary minus (one operand)
        System.out.print("(-");
        left.toLisp();
        System.out.print(")");
        break;
    }
  }
}