Funcs.cs

using System;

namespace Funcs {
  public static class Funcs {
    public static Func<A, C> Select<A, B, C>(this Func<A, B> f, Func<B, C> g) {
      return a => g(f(a));
    }

    public static Func<C, B> SelectMany<A, B, C>(this Func<C, A> f, Func<A, Func<C, B>> g) {
      return a => g(f(a))(a);
    }

    public static Func<C, D> SelectMany<A, B, C, D>(this Func<C, A> f, Func<A, Func<C, B>> p, Func<A, B, D> k) {
      return SelectMany<A, D, C>(f, b => Select<C, B, D>(p(b), x => k(b, x)));
    }

  }

  class UseFunc {
    Func<
      Func<A, B, C>
    , Func<int, A>
    , Func<int, B>
    , Func<int, C>
    >  
      use<A, B, C>() {
      return
        (f, a, b) =>
          from aa in a
          from bb in b
          select f(aa, bb);
    }
  }
}