gistfile1.cs

        public static Gen<ConsList<T>> Sequence<T>(this ConsList<Gen<T>> list)
        {
            if (list.IsNil) return Return(ConsList.Nil<T>());
            return list.Head.Bind(t =>
               list.Tail.Sequence().Bind(ts =>
                   Return(ts.Prepend(t))));
        }
        public static Gen<T> Return<T>(T value) => FromGenerator(rnd => value);
        public static Gen<TB> Ap<T, TB>(this Gen<Func<T, TB>> gf, Gen<T> gen) =>
            gf.Bind(f => gen.Bind(a => Return(f(a))));
        public static Gen<int> To(int max) => FromGenerator(rand => rand.GetInt % (max + 1));
        public static Gen<T> OneOf<T>(ConsList<Gen<T>> list) =>
            To(list.Count() - 1).Bind(n => list[n]);
        public static Gen<T> ElementOf<T>(ConsList<T> list) =>
            OneOf(list.Select(t => Return(t)).ToConsList());
        public static Gen<ConsList<T>> ListOf<T>(this Gen<T> gen, int n) =>
            Enumerable.Repeat(gen, n).ToConsList().Sequence();
        public static Gen<T> FromGenerator<T>(Func<ImmutableRandom, T> g) => new Gen<T>(g);
        public static T RunGen<T>(this Gen<T> gen, ImmutableRandom rand) => gen.generator(rand).Item1;