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Be a Functional Guide, not a Missionary

 

Posted on Thursday, October 5, 2017 11:43 PM

Stijn Moreels by Stijn Moreels

This post will expand on this subject in how I changed my way of writing code and how I became a functional guide.

Introduction

One of the things current Functional Programmers and Enthusiasts come across very often when working in a “mainstream” development environment, is that they must work together with non-functional programmers.

My opinion is that people should not try to convince other people of their opinion, but instead only show how you to do certain things and let the audience decide what they feel most comfortable with.

That’s exactly what happened to me, I worked on a project and because I used functional approaches; people asked me to explain some concepts that I introduced to the rest of the team.

Guidance

Instead of directly talking about Higher-Order Functions, Currying, Monads, Catamorphisms, Endomorphisms, … I decided that I wanted to start with the simplest thing I think was possible to change.

PipeTo

In functional programming, we try to compose all the functions together to create new functions. In imperative languages, we use variables that we can send to the next function instead of sending the result of the first function directly. Piping and Composition are those building blocks.

Note that Composition is the very root of all software development. It always feels to me that functional programming is using this all the way: Everything is an expression, and so, everything can be composed.

My first change was to add an extension method called ‘PipeTo’ in the C# project:

What piping really means to me, is just the order in which you express a value and a function. With piping, you can change that order. Normally we would type the method and then the argument that we want to send to that method.

What piping allows me to do, is to first write the value and then the method.

This simple extension allowed me to write quite powerful expressions:

This is some dummy example of how you can use this approach. Note that I use FsCheck as testing framework and that my test is actually expressed in a single line.

I see two major benefits about this approach:

  1. First, when I use this piping-method, I don’t have to express intermediate variables that sometimes only clutter the actual functionality you want to write. Together with the variables, in C# we must also express the types (if we don’t use ‘var’ everywhere); so, it struck me that I wasted time reading types instead of reading method names.
  1. Second, instead of assigning the result of a method to a variable, we can immediately send it to the next method. This allows us to write in the same order of the data flow like we would express this with intermediate variables.

To go a little deeper on the second benefit. This is what it looks like with the intermediate variables:

We need this intermediate variables to have the data flow from top to bottom (like you read a book). To get rid of the intermediate variabeles without the ‘PipeTo’, we could inline the variables:

But I hope that you find this less readable, that’s why we would extract this in separate variables for the same reason we can use the ‘PipeTo’: to have the data flow from top to bottom but still get that readability.

Maybe

In F#, we use the ‘Option’ type to indicate that a value might be missing. In Haskell we use ‘Maybe’. By default, in C# and other imperative languages, we use ‘null’ to indicate that there’s a value missing.

I’m not going explain fully why because that would lead us to far. There are many posts and books that will explain this you. Even the inventor of the ‘null’ type thought it was the ‘Billion Dolar Mistake’.

So, we use an other type to indicate this missing value. So what?

Well, this is very powerful and a lot more robust because now you now exactly where there’s a value present and where not. C# (for example) doesn’t have any such thing for reference types, but it got a less stronger type called ‘Nullable<>’ for value types.

My second change was to implement some basic functionality of the Maybe Monad.

The ‘Map’ in F# is the ‘Select’ in C#,
the ‘Filter’ in F# is the ‘Where’ in C#.

With this simple implementation, I’ve created some functionality that we can use to start implementing missing values with the ‘Maybe’ type.

The first thing I explained in this type, is the binding functionality. When you show people of endless ‘if’ structures that all would check ‘IsPresent’ on this type, you can show that this is exactly what the ‘Bind’ does:

Normally these ‘if’ structures would check for ‘null’. If we would use our already known practices of refactoring, we would see that there’s a duplication. The thing that’s variable is the action that must be executed when there’s a value. This is exactly what the ‘Bind’ method gets, so we could rewrite it like this:

The other two methods ‘Where’ and ‘Select’ must be familiar to you if you know LINQ. It’s strange to see that experienced C# developers know the functionality of LINQ but aren’t yet using the concepts behind LINQ in their own design. LINQ is functional programming.

The ‘Select’ takes the value from the ‘Maybe’ instance (if there is one) and execute a method that accepts this value. The return of the ‘Select’ is then a new ‘Maybe’ instance with the result of the just executed method.

The ‘Where’ takes a predicate and will return a ‘Maybe’ instance if the value is presents and the predicate holds for the value inside the ‘Maybe’.

This type itself isn’t functional, but what we do with it is; that’ why I think it’s also good first step into functional programming in C#.

 Extensions

I showed some examples of how we can achieve a more functional approach in an object-oriented language like C#. We can extend this idea and come up with even more extensions:

The first ones are probably the simplest. We define a foreach loop that we can use to run through a list of items and execute a (side-effect/dead-end) function on each one. We also define a ‘Tee’ that we can use to send a ‘dead-end’ function inside a pipeline. We don’t have to stop after our method returns ‘void’; we can just continue with the original value.

I also added a ‘Use’ extension to pipe a disposable resource and a ‘Compose’ extension to compose two functions together into a single function.

Now I think it would be a good exercise in functional programming to come up with some changes in your code that uses this extensions!

Conclusion

Instead of directly writing the software in a different language, with different keywords, syntax, practices, … I discovered that people are more comfortable if I use functional approaches first in the languages they're familiar with.

This way, you can clearly see in the same language syntax the “Before” and “After” part.

Remember, don’t try to convince other people of your opinion. Everyone has a different view and ways he or she works and feels comfortable. The only thing you can do, is show how you work and how you see things without blaming other languages or persons because they use a different approach.

Just like everything else, try to be open-minded!

Categories: Technology
written by: Stijn Moreels