Simple Functional Programming in C#

Some of the greatest crimes in modern computing are committed in the name of good object-orientated abstractions. Over time, a code base gets so polluted with abstract classes, factories and heavy dependencies on frameworks that a lot of it ends up serving as boilerplate to work around the rest. I’ve spent the last few months learning Haskell (A pure functional language) and Go (An imperative language that allows OO and functional styles) and it’s led me to the conclusion that John Carmack is right, sometimes all you really need is a function.

Go’s approach to OO struck me as very interesting because instead of complex class hierarchies they took a very simple approach and allowed you to associate a function with a type. There’s no this keyword, you assign the type a name and use that to access it’s properties. Here’s a very simple example:

Note: Unused variables are compile-time errors in Go, hence why this is much simpler than the upcoming C# examples.

We can do something similar in C#. Here’s a very simple OO example in C#. In pure OO, an object is a bundle of state and methods that operate on that state so I’m going with a contrived sample that demonstrates this.

Now lets look at the functional solution:

Note on line 2 we’ve given Tuples of type <string, string, int> the alias of Person. Since System.Tuple is a class, we create our Person tuple almost exactly the same way as our OO solution. The biggest difference is that there is no maintained state. Our CompareAge function takes two Person tuples and computes the required value. There’s also a lot less worrying about encapsulation, since we can explicitly see that our people tuples only exist in the scope where we create them.

I’ll expand on this post in the future with some more example of how aliasing types in C# can be used to write concise functional code. If you’d like to try this out, have a go at aliasing a list of Persons and writing a function that iterates over them and returns the total age of everyone (this is a classic example of a functional fold operation!)

I’m trying a more lean, agile approach to blogging because the tax on adding links and sources with my limited free time is too great and I don’t want to stop completely. If you want me to expand on anything in this post feel free to leave a comment or drop me a line and I’ll try my best.


Using C# code in PowerShell Scripts

Hi guys, very short post today! Since PowerShell has access to .NET framework assemblies, you can use C# code either from source *.cs files or embed it directly in your script like I’ve done here.

Then you can call on your C# methods using the following from the prompt:

PS > .\csharp_in_powershell.ps1
PS > [CSharpPSTest.PSTest]::Get()
Get Success: Default Value
PS > [CSharpPSTest.PSTest]::Set("New Value")
Set Success: New Value

If you’re using a lot of functions in your script then writing them in C# can be a good way to simplify the logic as right now there’s much better tool support available for C# than PowerShell. You can do a lot more with your C# code than what I’ve shown here but hopefully it’ll be a good starting point for you!