import pattpack.ast_vis2.*;
import pattpack.expr_vis2.*;
import java.io.*;

/**
 *  Driver for an Interpreter pattern example.
 *  This example refines and extends the Flyweight example,
 *  which in turn refined and extends the Composite example.
 *  It uses Singleton and Immutable patterns too.
 *  <PRE>
 *       Statement   ::= Assignment | Conditional | While | Compound | Output
 *       Assignment  ::= Var = Expr
 *       Conditional ::= if Expr then Statement else Statement
 *       While       ::= while Expr do Statement
 *       Compound    ::= begin Statement; ...; Statement end
 *       Output      ::= output Expr
 *  </PRE>
 *  The main method constructs the following program:
 *  <PRE>
 *       begin
 *         n = 5;
 *         output (n);
 *         fact = 1;
 *         while (n > 1) do
 *           begin
 *             fact := fact * n;
 *             n := n - 1
 *           end;
 *         output (fact)
 *       end
 *  </PRE>
 *  It then interprets and/or pretty prints it.
 */
public class Main {
    /** 
     *  Usual entry point.
     *  Constructs an example program.
     *  Interpret and/or pretty print the example program.
     */
    public static void main (String [] arg) {
	VarFactory vf = VarFactory.getInstance ();
	Compound factorial = new Compound ( 
	    new Statement [] {
		new Assignment (vf.makeVar ("n"), vf.makeVar (6)),
		new Output (vf.makeVar ("n")),
		new Assignment (vf.makeVar ("fact"), vf.makeVar (1)),
		new While (
		    new Gt (vf.makeVar ("n"), vf.makeVar (1)),
			new Compound (
			    new Assignment (vf.makeVar ("fact"),
					    new Mul (vf.makeVar ("fact"),
						     vf.makeVar ("n"))),
			    new Assignment (vf.makeVar ("n"),
					    new Sub (vf.makeVar ("n"),
						     vf.makeVar (1))))),
		new Output (vf.makeVar ("fact")), });
	//+1 PrintVisitor pv = new PrintVisitor (System.out);
	//+1 pv.visit (factorial, new Integer (0));
	//+1 System.out.println ();
	InterpretVisitor iv = new InterpretVisitor ();
	iv.visit (factorial, null);
    }
}