Integration/end-to-end testing is considered one of the best indicators that your code functions correctly, and everything is wired up as it should. Testcontainers is a wonderful library for creating and running embeddable Docker containers that can run alongside your tests, so you can have real implementations of your third-party dependencies, instead of relying on fragile mocks. Testcontainers is a mature Java library that comes out of the box with integrations for Postgres, Kafka, RabbitMQ, and many more, as well as support for many test runners and even ports to other languages.

In this short post, I’ll explain how to integrate Testcontainers (the Scala flavor) to play nicely with ZIO Test, showcasing some of the great composability features ZIO provides.

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A few days ago I tweeted a C# code snippet, showing a FizzBuzz implementation using some of the new features in C# 8.0. The tweet “went viral”, as the kids say, with several people admiring the terse and functional aspect of it, while others asked me why I wasn’t writing it in F# in the first place?

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Over the past two years, the PDF version of Bartosz Milewski’s Category Theory for Programmers became a highly-successful open-source book, which was adapted to other programming languages, such as Scala and OCaml. Unfortunately, building this 400+ page PDF from LaTeX sources in multiple editions took a significant amount of time, sometimes upwards of 15 minutes. One of the reasons was, all the code snippets are loaded from external code files (so that they can be easily adapted to other programming languages), and they have to be compiled each time in a format LaTeX understands.

I recently explored some possibilities to reduce the time it takes for the snippets to build, and I’m happy to report the results: a 60% improvement overall! Big thanks to muzimuzhi from the minted github, who generously helped me to arrive at the solution below.

Here’s a quick summary of my changes, that resulted in reducing my Travis CI builds from 14-16 minutes to mere 6!

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This was initially a long post, detailing all the manual steps required to set up a complete Haskell development environment, however, thanks to a hint by Krzysztof Cieślak, this process is now fully automated, allowing you to get started in minutes. All thanks to a Visual Studio Code feature called devcontainers, supporting running the development environment in a Docker container.

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There’s a fantastic free online course (MOOC) for the Russian-speaking developer community on Stepik for learning Haskell - a two-part course titled Functional Programming in Haskell by Denis Moskvin, (then) associate professor at the St. Petersburg Academic University. I recently re-watched the course (having completed it previously) and decided to take notes and summarize the course content in English for your enjoyment.

I would like to thank Denis Moskvin for providing this amazing resource for free, and urge you, if you speak Russian and want to learn Haskell, to work through the course material and exercises!

Below is the summary of the first module, Introduction, out of 5.

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It’s amazing how sometimes just having a different framing of the problem helps with developing a much deeper understanding of the problem. I was working through the exercises of the Data61 Functional Programming course, assisted by Brian McKenna’s video streams, and I came accross a definition of a right fold that can be thought of as “constructor replacement”:

The expression foldr f z list replaces in list:

  1. Every occurence of the cons constructor (:) with f
  2. Any occurrence of the nil constructor [] with z
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The book The Pragmatic Programmer: From Journeyman to Master by Andy Hunt and Dave Thomas suggests that as developers, we should “learn at least one new language every year.” (pg. 14)

When I recently asked a roomful of developers, if there’s anyone who had learned a new language this year, only very few hands went up. A year ago today, that would have been me in the audience, keeping my hands down.

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Original title was “Monads solve a problem you might not have, but it’s a nice problem to have”, which is an homage to a great post by Krzysztof Koźmic about IoC containers.

I can’t think of another 5-letter word that strikes fear in the hearts of so many developers, coming from an object-oriended/imperative language to a functional one. So much so, this, and other M-words are outright banned on some resources.

This post will not attempt to explain monads, at least, not on purpose. This fantastic post by Max Kreminski does this better than I ever could - by showing that most “monad tutorials” (or, educational blog posts in general) have problem-solution ordering issues. Please take a moment to read this wonderful post before continuing.

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