Main {{
  public static void p(String s){ System.out.print(s); }
  public static void main(String args[]) throws Exception {
    Start start = Start.parse(System.in); 
    // some sample functionality
    p(start.display() + "\n");
    p(start.print() + "\n");
    p(start.toStr() + "\n");
    System.out.println(start.equals(start));
    p(start.magic().display() + "\n");
  }
}}

Start {{
  // magically replace apples by oranges and vice versa
  // and keep the rest of the structure the same
  public Start magic() {
    return new Traversal(new Bc(){
      // B combine(Literal l){return new B(l.isPositive2());}
      B combine(Literal l){return new B(l.isPositive());}
    }).<Start> traverse(this);
  }
}}


Literal {{
boolean isPositive() {
  return new Traversal(new ID() {
      // assume one Pos in first field of Literal
      boolean combine(Pos pos) {return true;}
      // boolean combine() {return false;}
      boolean combine(Neg neg) {return false;}
      boolean combine(Literal o, boolean s) { return s; }
      // boolean combine(Object o, boolean s) { return s; }
  }, Control.bypass("gen.Literal.var")).<Boolean> traverse(this);
  // nicer: Control.strategy("Literal -> Pos")
}
}}


Literal {{
boolean isPositive2() {
  return value.isPositive(); }
}}
Sign{{
abstract boolean isPositive();
}}
Pos{{ 
boolean isPositive(){ return true;}
}}
Neg {{
boolean isPositive(){ return false;}
}}