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IO monad: which, why and how

In many discussions about FP - especially about purely functional programming - there are talks about IO monad, IO type and so on. Its users’ argument on how it is better than your standard imperative approach, how it helps reason, encapsulate side-effects and design more elegant programs. On the other hand, its opponents argue, that programs are side-effectful by nature, so you would end up with something that needs IO for like 80% of the codebase while learning curve for newcomers would go up, so what the benefit? Let’s try to figure out.

AST playground: recursion schemes and recursive data

So, we parsed an input - file, stream of characters or string - and we got a nicely structured data in the form of a tree and/or an algebraic data type. What now?

From String to AST: parsing

Whether you have to do with data in form of CSV, JSON or a full-blooded programming language like C, JavaScript, Scala, or maybe a query language like SQL, you always transform some sequence of characters (or binary values) into a structured representation. Whatever you’ll do with that representation depends on your domain and business goals, and is quite often the core value of whatever you are doing. With a plethora of tools doing the parsing for us (including the error-handling), we might easily overlook how complex and interesting process it is.

ADT through the looking glass - lenses, prims and other optics

Algebraic data structures and invaluable in functional programming. With immutable data structures reasoning about the code is easy. Concurrency requires little effort as you don’t have to be worried about locking, mutexes and semaphores - nobody can change your data anyway. If you need to update something you can just create an updated copy and use it for now on. Except if you have a nested structure and need to update something deep, deep inside.

Different ways to understand a monad

As soon as you start mentioning functional programming, monads pops out as something that you have to know. However, hardly anyone is good at explaining what a monad is. That is why we’ll try to get some intuition about it without defining it.

The F-words: functor and friends

While algebras are something we (programmers) rely on in our everyday work, we don’t always use them knowingly. Functional programming, however, has a relatively high number of programmers, that care about correctness and mathematical formalism, that leads to it.It is no surprise that it was FP that explored the idea that if you perceive your program as a pipeline of operations, you could provide stronger guarantees if you had a tools to define such pipelines mathematically.

Algebras we love

If you work with anything that can be modeled mathematically, you most likely know that many things you work can be expressed with algebras. However, if you are not a graduate of a computer science course or similar you might not know how ubiquitous they are and how often you rely on some of them. (And I don’t mean F-algebras and FP-concepts). So what are algebras and where can we meet some most common of them?

It's all about relations

In FP we talk a lot about algebras functions and types. But types are sets and functions are also sets. Algebras are types with operations, that fulfill some conditions, which means also sets. So how low should we get if we want to start from the beginning? I would say we should start with finitary relations.

In the beginning, there was the empty set

What would you say if I told you that in math everything is a set? That, whatever mathematical object you name, it can be defined using sets? And not sets, that contains some special ingredient somewhere deep inside - but by basically wrapping up empty sets and merging it with more wrapped empty sets in various degree of wrapping?

Kinds of types in Scala, part 3: embedding some more info in a type

In the previous post, we understood how parametric types work, which let cover most of the cases we’ll have in our everyday coding. However, there are some interesting concepts, which, while not so heavily used, can come handy at a time.

Kinds of types in Scala, part 2: take type, return type or type parameters

In the previous post, we laid the foundation for understanding the type system in Scala. But concrete types only would be too little to make language truly expressive. So, now we’ll try to parametrize it.

Kinds of types in Scala, part 1: types, what are they?

When I try to explain to someone why I prefer Scala to Java, and why functional programming works better with Scala, one of the arguments is that is has a better type system. But what exactly it means? What advantage it has over the static type of languages like Java or Go?

My issues with Swagger

As far as I can tell, Swagger has 2 main use cases: it’s a specification you can use to scaffold your client/server or a live documentation generated from an existing implementation. I have an issue with the latter when it comes to Akka HTTP.

Implicits, type classes, and extension methods, part 4: understanding implicits

In previous posts, we covered most popular implicit use cases. What is left to complete the picture is the implicits mechanics itself.

Implicits, type classes, and extension methods, part 3: conversions and implicit-based patterns

In previous posts, we covered the most basic use cases of implicits. However, to complete the image we not only need to understand how they can provide instances but also how they can transform them. Once we understand that, we can talk a bit about some patterns that combine both implicit parameters and conversions.

Implicits, type classes, and extension methods, part 2: implicit derivation

In the previous post, we learned a bit about type classes, as they were the major reason for introducing the mechanism. We could see that it is a great way of implementing the open-closed principle in a functional way: while the existing implementations are unchanged we can extend the behavior for new types. We haven’t seen though how to address one issue with them: how to provide behavior for potentially thousands of cases?

Implicits, type classes, and extension methods, part 1: with type classes in mind

Implicits. For some people, they are an indispensable feature of Scala, that allows achieving otherwise impossible things. For others a sole reason to avoid using the language. As far as I can tell the majority of the later never really learned how to use them right.

Reflections on using Typelevel Scala

At some point, Typelevel decided to fork Scala in order to test feature that it’s members found useful and get feedback on these features without the need for waiting for next official Scala release. Latest such version was Typelevel Scala 4 based on Lightbend Scala 2.12.4, which I decided to use at some point. Now, that everyone is migrating on 2.12.6 I can tell: what TL Scala give me for all that time?

sbt tips and tricks

In previous posts (#1, #2) I described a bit of theory about using sbt. However, besides long, heavy topics there are also some smaller pieces of knowledge, that you can find useful. Most of them should be obvious for people, who use sbt a little bit longer, but I decided to gather these tips here nonetheless.

Speed up things in scalac and sbt

Scala is not the fastest language to compile. sbt adds its own overhead. So in a life of most (every?) business applications written in Scala, CI build is so long, that after git push you can go watch next episode of a TV show. Local changes take ages, even with Zinc. And you don’t want to rewrite half the stuff not has the budget for considering things like Triplequote Hydra. What then?

Relearn your sbt

When I started to learn sbt, I noticed, that there is a huge gap between how I’m told to write builds for simple projects and how I have to write them when I maintain complex multi-module monstrosity. After a while I came to conclusion, that very often the way we are writing build.sbt is but a cargo cult programming.

Scala FUD FAQ for newbies

When I browse Reddit, read Hacker News comments or google for Scala-related topics I sometimes find some misconceptions. These are not about: what is monad or how to start using Cats, as people asking this kind of questions already have some basic knowledge about what they want to learn.

Adventures with custom Predef

I first heard about custom Predef from Paweł Szulc. I don’t remember exact circumstances, but I think it was soon after he started working at Slam Data on Quasar. Apparently, in all of their projects, they decided to use own Predef instead of Scala’s build in. But what does that mean? Why one would consider it, and what would be the consequences?

Tagged or AnyVal?

When we want to better describe our domain, at some point we might want to start using types for describing what each value means. String, Int or Double tell us everything about what could we do with a value, but does it really explain context?

Ammonite + Uberjar = Domain Shell

I had an issue, when on my test server I had to modify some values. I could log in directly into database, but I didn’t want to. I could use REST API, but not all services are mapped to endpoints (and for a good reason!). Nonetheless, sometimes I needed to call them.

Setting up Mattermost

When you live far away from some of your best friends, you want to find some reasonable ways to stay in touch. After a while, we found out that social media and instant messaging apps are not really an answer to our needs, so we decided to give a chance to something that easily engages everyone. Most, if not all, of us, know about Slack and how it (usually) improves communication within teams that use it. However, if you want to fully own your data and e.g. have access to all archives without high pricing, you might start with some cheaper alternative. It appears there is one - Mattermost Team Edition. And that’s what we decided to try out.

Improving your project with SBT

I believe that the work on keeping quality high should start from the very beginning of the project. When it comes to actual implementation setting up build configuration is the very first thing one makes. The choice of tools has a huge impact on the process and results.