Don't Break The Build .Net Tutorials

The B-Combinator In C#

My last post was implementing the K combinator in C# as an extension method. Today, I am moving on to the B-Combinator. The B combinator has the form:

The code that I will show can be used on any collection that implements the IEnumerable interface. Here we go:

public static IEnumerable<T> b<T>(this IEnumerable<T> me, Func<T, T> f, Func<T, T> g)
{
    List<T> output = new List<T>();
    foreach (var i in me)
    {
        output.Add(f(g(i)));
    }

    return output.AsEnumerable<T>();
}

First off, it is important to note which namespaces we will need to include (I hate when I have to google or guess since the writer doesn't include them in the tutorial/post). This one is nice and easy and only requires:

• System.Collections.Generic
• System.Linq

Now, to examine the code. The first line is:

public static IEnumerable<T> b<T>(this IEnumerable<T> me, Func<T, T> f, Func<T, T> g)

Next comes:

List<T> output = new List<T>();
foreach (var i in me)
{
    output.Add(f(g(i)));
}
return output.AsEnumerable<T>();

int[] numbers = { 1, 2, 3, 4, 5 };
numbers.b(x => (x * 5), x => (x - 3));

/* Output: -10, -5, 0, 5, 10 */