No Sugar, please

As a software developer I always strive to get better. I try to learn at least one new language per year. I found it a good second step to get into some kind of Kata routine with a new language that I just picked up. It’s a good exercise on the path of getting literate in a new programming language to solve the same (simple) problem over and over again. 

In reference to Japanese culture that is often called a Kata. I have made it a habit to start my day doing at least one Kata. The trick is to try to find a different solution every time. The first ten to fifteen different solutions may be easy. But coming to your 80th solution will be interesting. You might end up using TensorFlow since you are out of real ideas.

If you have not yet discovered exercism.io I highly recommend having a look! It provides multiple dozens of Katas for every language you might be interested in. It also provides a mentored track for each language that allows a mentor to nit pick our solution and thus provides another layer of improvement on your coding skills. Furthermore that is an excellent space to discus patterns and language idiomatics.

I lately tried a new approach in Katas. Instead of solving the problems in a different way, I take previous solutions and desugar them. Desugaring is the process of removing syntactic sugar your language provides.

Let’s have the simplest example and desugar “Hello, World!”:

Desugared:

I personally find the desugared example even more intuitive and easy to understand. It helps me to understand the monadic computation and binding from getLine to name to the call of putStrLn. But we can drive this further.

Infix notation is also syntactic sugar. Haskell is a functional language. That means everything is a function. And functions are just data. So let’s desugar “Hello, World!” further, to have a look at that:

Oh, look! Haskell is a LISP! Now things fall into places I have not seen them, yet.

Let’s try desugaring another Kata that might not be as trivial as “Hello, World!”. 

Taken directly from exercism.io: "Given a number n, determine what the nth prime is. By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13. If your language provides methods in the standard library to deal with prime numbers, pretend they don’t exist and implement them yourself."

Ok, let's do this.  A solution to the nth-prime-Kata could look like the following:

Let’s desugar that bit by bit and see, what we might learn. I start with the nth’ function since it might be where the meat is. nth is merely an interface.

At wirst let’s have a look at the signature.

Since Haskell is a purely functional language and a function is always a mapping from a -> b, we can see that this is actually a composed function. Desugaring that will give a clear understanding on how the type signature works:

Oh, wow! The type signature makes sense now!

Next to the guards; that are those pipe characters. They are indeed a shorthand for if-then-else what itself is sugar on case. So

becomes

Following that we see an if-block. We know, what to do with that!

becomes

Pretty neat! We learned that case is the foundation of all branching operations in Haskell. Good to know!

The next interesting thing is where. This is not that interesting, since it is only a search and replace operation. But we have something in the following clause that catches our attention while doing that: We have a list comprehension:

We read this as “make a list from all x of primes that are natural dividers of c". That clearly is a nice bit of syntactic sugar. Let’s try to desugar that (in two steps):

That is very interesting. We learned that list comprehension has a monadic structure.

Bringing it all together we get this desugared version of our nth’:

This is not pretty. It's really 'bitter', you might even say. But we learned a lot about the language. Haskell is in its very core a purely functional language with very little actual vocabulary to it. As we dive deeper in desugaring the syntax we will manifest the principles on which the language is built upon.

The motivation to this article is to get you interested in the fundamentals and principles of your own language of choice. Try desugaring short programs in your language and watch the principles blossom. Try to understand, why things are that way and then slowly reapply the sugar one bit at a time.

Go to exercism.io if you haven’t done that, yet.

You can find some of my exercism.io solutions for the Haskell track on GitHub: https://github.com/felbit/exercise-haskell