Modelling API Responses With sbt-json – Print Current Bitcoin Price

I’m currently working on an sbt plugin that generates Scala case classes at compile time to model JSON API responses for easy deserialization especially with the Scala play-json library.

The plugin makes it possible to access JSON documents in a statically typed way including auto-completion. It takes a sample JSON document as input (either from a file or a URL) and generates Scala types that can be used to read data with the same structure.

Let’s look at a basic example of an app that can print the current Bitcoin price to the console.

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A new Scala feature for making illegal states unrepresentable

Making illegal states unrepresentable means that we enforce invariants on the code that we write, and choose data types so that states that are invalid won’t show up in our programs. 1

By reducing the number of representable wrong states we also reduce the number of potential bugs in our program by a great deal, as well as the number of tests needed to check for invalid inputs and outputs.

If we can’t create an illegal argument of a given type, we don’t need test cases for this illegal state for any function that takes arguments of that type as inputs.

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12 Things You Should Know About Event Sourcing

Are you aware that storing and updating current state means loosing important data?

Event sourcing is a way to solve this problem. It is the technique of storing state transitions rather than updating the current state itself.

Event sourcing has some more benefits:

  • Complete audit-proof log for free
  • Complete history of every state change ever
  • No more mapping objects to tables
  • Distribution support
  • CQRS (Command Query Responsibility Segregation) support
  • Natural fit for domain-driven design and functional programming
  • Be prepared for unanticipated use cases in the future (for free)

State transitions are an important part of our problem space and should be modelled within our domain — Greg Young

When I first encountered the concept of event sourcing and CQRS and looked at some sample applications, I had the impression that it must be extremely difficult to implement. But later I found out that event sourcing is easier than I first thought, especially when it is expressed with functional programming.

Here are 12 things about event sourcing that should help you to get started today.

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What are Scala Type Classes?

What are Scala type classes, what kind of problem do they solve and how are they implemented?

In a nut shell, type classes provide polymorphism without using subtyping, but in a completely type safe way.

Type classes represent some common functionality that can be applied to values of many different types. Moreover, we don’t have to change existing types in order to extend them with the new functionality.

In this post I will describe 5 simple steps for encoding a type class in Scala in an idiomatic way.

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7 Most Convenient Ways To Create A Future Either Stack

In Scala Future[A] and Either[A, B] are very useful and commonly used types. Very often we want to combine them, but a Future[Either[A, B]] is kind of awkward to handle not only because we don’t want to have to call Await anywhere.

One way to deal with this is to stack the types into a combined data type EitherT defined in Cats that is much easier to handle.

Still it can be quite unwieldy to compose values of this new type with other values of different types.

To get nice composability (e.g. with for comprehensions) we have to wrap other values into the new type by lifting them up inside the monad stack.

Here are the most convenient ways that I found to do that.
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Up your game by stacking Applicatives in Scala

Monads are very useful in many different situations.

But they get a little unwieldy when we have different Monads nested inside each other.

In these cases Monad Transformers come to the rescue. They allow us to compose different Monads into one that shares the functionalities of all of them.

But sometimes we want to combine the behavior of Applicatives in the same way. This is especially useful when we have to combine independent tasks.

In this post we will see how to do this in Scala with the use of the Cats library.

But let’s first look at an example of Monad Transformers.

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Hands on Monoids in Scala – Applying categories to birdwatching

What do Monoids in Scala have to do with birdwatching?

Before I come to that I would like to mention that since I’m coming from F# and recently started with Scala, being able to use type classes in my code is new to me.

I find this really exciting which I’d like to share.

So this post is maybe not a complete cohesive tutorial an Monoids but I hope that it is a fun little teaser for looking into things like functional programming, Scala, Cats, Haskell, type classes or maybe even category theory.

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