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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. ...

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? ...

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? ...

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 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? ...

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. ...