Everything has a cost. Some costs are obvious. Money costs, time costs, overhead costs. Most, but not all, apply to writing tests for your software.

Higher order functions are functions that accept other functions as parameters. Higher kinded types are types that can accept other types as parameters. In Scala, the syntax F[_] is used to express that F is a higher-kinded type that can accept any type.

Three ways to do functional programming when working with the Play Framework.

I've spent the last year using AWS DynamoDB at work. When we initially searched for a Scala client for DynamoDB, we had the following criteria:

• Good for Scala beginners
• Up to date
• Well documented

Sadly, none of the Scala libraries available at that time matched all three criteria. The most up-to-date libraries were not suitable for a team starting out with Scala and DynamoDB. The most beginner-friendly libraries were out-of-date, and most only had superficial documentation.

This blog post differs from my usual ones; I'm writing it as I learn something. As such, it is more of a story that contains errors and misunderstanding than a factual blog post.

Using custom types in Play Framework’s routes file is a major win, and is not something obviously supported.

Scala has nice abstractions for asynchronous code. However, writing tests for that code sometimes results in an ugly, unreadable mess. Fortunately, ScalaTest has built-in support for testing Futures, in addition to utilities for other types of asynchronous testing, such as polling and test-probes.

In abstract algebra, a branch of mathematics, a monoid is an algebraic structure with a single associative binary operation and an identity element. Monoids are studied in semigroup theory as they are semigroups with identity.

Wikipedia has the above definition of a Monoid. This blog post will desconstruct that definition to simply describe what a monoid is, and why you would want to use one.

Aggregation services (sometimes known as Composite or Hydration services) are useful when working in SOA. In SOA, services are responsible for discrete objects and collections, yet still often need to reference other object or collections controlled by another service. This is done via referencing Ids. In order to display something useful to the user it is necessary to lookup data from multiple sources and aggregate them together.

Working out the Fibonacci numbers are a standard exercise when learning a programming language, or just refreshing your knowledge. This is a recap of various ways to calculate them in Scala. All the code is available in a handy gist.

I've been using Akka Camel and ActiveMQ recently, as part of a delayed worker-queue system. Given the lack of good googleable information about combining the two, I thought it would be useful if I explained briefly how to get Akka Camel and ActiveMQ to work together in the form of a quick example.

Using a DSL to write a test can prove to be useful, especially when there are lots of prerequisites, or the problem is complex. Having a test that is incredibly readable reduces complexity overhead and aids reader comprehension. Any tests that require the reader to retain a mental map could benefit from a DSL.

Scala has three different frameworks for writing unit tests, JUnit, Specs2 and ScalaTest. I have mainly been using ScalaTest since I started to learn Scala about four months ago. One of the areas I have been concentrating on is how to write good assertions. Specifically, ones that yield easily diagnosable error messages when they fail.