// This code requires Intermediate Java and the prof2.plt
// (or later) patch

class Posn {
  double x;
  double y;
  Posn(double x, double y) {
    this.x = x; this.y = y;
  }
  public boolean equals(Object o) {
    // See the slides for the improvement
    // using Advanced Java's instanceof 
    return (this.x == ((Posn)o).x)
           && (this.y == ((Posn)o).y);
  }
}

abstract class List {
  abstract boolean isMember(Object o);
  abstract Object nth(int n);
}
 
class Empty extends List {
  Empty() { }
  boolean isMember(Object o) { return false; }
  Object nth(int n) { return new Empty(); }
}
 
class Cons extends List {
  Object first;
  List rest;
  Cons(Object first, List rest) {
   this.first = first; this.rest = rest;
  }
  boolean isMember(Object o) {
    return this.first.equals(o) || this.rest.isMember(o);
  }
  Object nth(int n) {
    if (n == 0)
      return this.first;
    else
      return this.rest.nth(n-1);
  }
}

// ----------------------------------------

interface NamedPlace {
  boolean isNice();
}

abstract class Door {
  abstract List places();
} 

class Escape extends Door implements NamedPlace {
  String name;
  Escape(String name) {
    this.name = name;
  }
  List places() {
    return new Cons(this, new Empty());
  }
  boolean isNice() {
    return !this.name.equals("mars");
  }
}

class Into extends Door {
  Room next;
  Into(Room next) {
    this.next = next;
  }
  List places() {
    return this.next.places();
  }
}

class NamedInto extends Into implements NamedPlace {
  String name;
  NamedInto(Room next, String name) {
    super(next);
    this.name = name;
  }
  List places() {
    return new Cons(this, super.places());
  }
  boolean isNice() { return true; }
}

class Short extends Into {
  double height;
  Short(Room next, double height) {
    super(next);
    this.height = height;
  }
}


class Room {
  Door left;
  Door right;
  Room(Door left, Door right) {
   this.left = left;
   this.right = right;
  }
  List places() {
    List l = this.left.places();
    List r = this.right.places();
    return l.append(r);
  }
}

class Person {
  String dest;
  double height;
  Person(String dest, double height) {
    this.dest = dest;
    this.height = height;
  }
  boolean isDest(String s) {
    return this.dest.equals(s);
  }
}

// The Factory class helps in writing tests:
//  new Factory().Example().escapePath(new Person("mars", 1))
class Factory {
  Factory() { }
  Room Example() {
    Door meadow = new Escape("meadow");
    Door street = new Escape("street");
    Room ms = new Room(meadow, street);
    Room planets = new Room(new Escape("mars"),
                            new Escape("venus"));
    return new Room(new NamedInto(ms, "crossing"),
                    new Short(planets, 1));
  }
}

// ----------------------------------------

abstract class List {
  abstract boolean isMember(Object o);
  abstract List append(List l);
}
 
class Empty extends List {
  Empty() { }
  boolean isMember(Object o) { return false; }
  List append(List l) { return l; }
}
 
class Cons extends List {
  Object first;
  List rest;
  Cons(Object first, List rest) {
   this.first = first; this.rest = rest;
  }
  boolean isMember(Object o) {
    return this.first.equals(o) || this.rest.isMember(o);
  }
  List append(List l) {
    return new Cons(this.first,
                    this.rest.append(l));
  }
}