In functional programming, pattern matching is a form of dispatch to choose the correct variant of the functions to be called. It's actually inspired by a standard mathematical notation with the syntax to express conditional execution. We can start our discussion on matching pattern by borrowing the code from Chapter 1, Tasting Functional Style in C#, when we talked about recursion. The following is the GetFactorial() functional we used to retrieve a factorial value:

public partial class Program 
{ 
  private static intGetFactorial(intintNumber) 
  { 
    if (intNumber == 0) 
    { 
      return 1; 
    } 
    returnintNumber * GetFactorial(intNumber - 1); 
  } 
} 

As we can see in the preceding code, it gives us two definitions. In this case, the dispatcher is chosen based on whether the actual intNumber parameter pattern matches 0 or not. The use of the pattern matching are closer to this if conditional expression since we...