Filterable.hx

interface Filterable<M, A> {
   public function filter (f:A->Bool):Of<M,A>;
}

class MyArray<A> implements Filterable<MyArray<In>, A> {
   var a:Array<A>;
   public function new (?a:Array<A>) {
     this.a = a == null ? [] else a;
   }
   public function filter(f:A->Bool):MyArray<A> {
      return new MyArray(a.filter(f));
   }
}

class MyList<A> implements Filterable<MyList<In>, A> 
{
   var a:List<A>;
   public function new () {
     this.a = a == null ? new List() else a;
   }
   public function filter(f:A->Bool):MyList<A> {
      return new MyList(a.filter(f));
   }
}

class Main {
  // abstract over the type constructor
  public static function withFilterable <M>(m:Filterable<M, Int>):Of<M,Int> 
  {
    return m.filter(function (x) return x > 10);
  }

  public static function main () {
     trace(withFilterable(new MyArray())); // the result is typed as MyArray<Int>
     trace(withFilterable(new MyList())); // the result is typed as MyList<Int>
  }

}