using System;
using Xunit;

namespace Category
{
    public static class CategoryExtensions
    {
        public static Func<A, C> Compose<A, B, C>(this Func<B, C> g, Func<A, B> f)
        {
            return x => g(f(x));
        }
    }
    public class CategoryTest
    {
        Func<int, bool> f = (int i) => i % 2 == 0;

        Func<bool, string> g = (bool b) => b ? "True" : "False";

        [Theory]
        [InlineData(2, "True")]
        [InlineData(3, "False")]
        public void Composition(int input, string output)
        {
            Func<int, string> composed = g.Compose(f);

            Assert.Equal(composed(input), output);
        }
    }
}