public class Comb<A, B> implements F<A, Comb<A, B>> {
  private final B b;
  private final Semigroup<B> m;
  private final F<A, B> f;

  private Comb(final Semigroup<B> m, final F<A, B> f, final B b) {
    this.f = f;
    this.m = m;
    this.b = b;
  }

  public static <A, B> Comb<A, B> comb(final F<A, B> f, final Monoid<B> m) {
    return new Comb<A, B>(m.semigroup(), f, m.zero());
  }

  public static <A, B> Comb<A, B> comb(final F<A, B> f, final Semigroup<B> m, final B b) {
    return new Comb<A, B>(m, f, b);
  }

  public Comb<A, B> f(final A a) {
    return comb(f, m, m.sum(b, f.f(a)));
  }
}