Functional C# for Beginners

FunctionalCSharpNotebook.cs

// Instead of 

public static int Add(int x, int y) {
  return x + y;
}

// Use a lambda to add two sums
public static int Add(int x, int y) => x + y;

// Func is a delegate that can reference anything with that param signature.  
// Delegates are just variables that point to functions rather than values.
// We could easily switch the Add() method for a Subtract() one here.
Func<int, int, int> Operation = Add;

// Prints 238.
Console.WriteLine(Operation(5, 233));

////////////////////////////////////////

// This func doesn't capture anything outside, so it will be treated as a method call.
// It also creates a functor, just an empty one and it is not recreated.
// A functor is a design pattern that allows for a generic type to apply a function 
// inside without changing the structure of the generic type.
Func<string, string> UpperCase = str => str.ToUpper();

// Prints "HEY"
Console.WriteLine(UpperCase("Hey"));

////////////////////////////////////////

IEnumerable<int> squares =
    // Use higher order functions to square items in a list
    // (Select can also be thought of as Map).
    Enumerable.Range(1, 5).Select(value => value * value);   

// Prints 1 4 9 16 25 on newlines.
foreach (var square in squares) {
    Console.WriteLine(square);
}