import junit.framework.*;

public class ListTest extends TestCase {
  public ListTest(String name) {
    super(name);
  }
  
  public void testEmptyToString() {
    assertEquals("empty toString", "[ ]", Empty.ONLY.toString());
  }
  
  public void testConsToString() {
    List list = new Cons(3, new Cons(4, Empty.ONLY));
    assertEquals("cons toString",
                 "[ 3 4 ]",
                 list.toString());
  }
  
  public void testEmptyToStringHelp() {
    assertEquals("empty help", "", Empty.ONLY.toStringHelp());
  }
  
  public void testConsToStringHelp() {
    List list = new Cons(3, new Cons(1, Empty.ONLY));
    assertEquals("cons help", "3 1 ", list.toStringHelp());
  }
}

abstract class List {
  public String toString() {
    return "[ " + toStringHelp() + "]";
  }
  
  abstract String toStringHelp();
}

class Empty extends List {
  public static final Empty ONLY = new Empty();
  
  private Empty() {}
  
  public String toStringHelp() {
    return "";
  }
}

class Cons extends List {
  int first;
  List rest;
  
  Cons(int f, List r) {
    first = f;
    rest = r;
  }
  
  public String toStringHelp() {
    return first + " " + rest.toStringHelp();
  }
}