public abstract class Expr {

    abstract Expr eval();
    abstract Expr call(String method, Expr[] es);
    public static void main(String[] s) {
	Expr e1 = new Call("plus", 
			  new Call("mult", new Int(1), new Expr[] {new Int(2)}),
                          new Expr[] {new Int(3)});
	System.out.println("Eval " + e1 + " = " + e1.eval());
	Expr e2 = new Call("plus", new Int(1), 
			   new Expr[] {
			       new Call("mult", new Int(2), 
					new Expr[] {new Int(3)})});
	System.out.println("Eval " + e2 + " = " + e2.eval());
    }

}

abstract class Obj extends Expr {
    Expr eval() {
	return this;
    }
	
}

class Int extends Obj {
    int x;
    Int(int x) {
	this.x = x;
    }
    Expr call(String method, Expr[] es) {
	if ("plus".equals(method)) {
            Expr e = es[0].eval();
            if (e instanceof Int) {
		return new Int(x + ((Int) e).x);
	    }
	}
	if ("mult".equals(method)) {
            Expr e = es[0].eval();
            if (e instanceof Int) {
		return new Int(x * ((Int) e).x);
	    }
	}
	return null;
    }
    public String toString() {
	return "" + x;
    }
}

class Call extends Expr {
    String method;
    Expr obj;
    Expr[] params;
    Call(String method, Expr obj, Expr[] params) {
	this.method = method;
        this.obj = obj;
        this.params = params;
    }
    Expr eval() {
        Expr[] evals = new Expr[params.length];
        for (int i = 0; i < evals.length; i++) {
	    evals[i] = params[i].eval();
	}
        return obj.eval().call(method, evals);
    }
    Expr call(String method, Expr[] es) {
	return null;
    }
    public String toString() {
	String res = obj + "." + method + "(";
	for (int i = 0; i < params.length - 1; i++) {
	    res += params[i] + ", ";
        }
        if (params.length != 0) {
	    res += params[params.length - 1];
	}
	res += ")";
        return res;
    }

}