Me: Simple! First we sum all the raw charges. Then we sum the totals over all categories - the two should be equal.
Computer: … Nope!
Me: What?! Let me see… Are you telling me that -0.01 + -0.05 is different from -0.06?!
Computer: Yep!

That’s how I learned (again) to never use doubles for monetary amounts. I would never have thought of it myself (though I should have), hadn’t we used generative testing to produce random test data (popular troublemakers included) - data I wouldn’t have thought of, such as 0.01 + 0.05 that cannot be represented precisely with a double. Now that we switched safely over to BigDecimals and angry customers and law suits are off the table, you might wonder what is this generative testing about and how does it work.

Instead of hardcoding inputs and expected outputs, as in the traditional “example-based” testing, inputs are randomly generated and outputs are checked against rules (“properties”) that you define, such as “the output of (sort list) should have the same elements and length as list; also, each element is >= its predecessor”. And you can generate as many inputs as you want, for instance 100 is a popular choice.

I have just gone through the painful experience of troubleshooting a remote Java webapp in a production-like environment and longed for Clojure’s explore-and-edit-running-app REPL. I want to demonstrate and contrast the tools the two languages offer for this case.

As a Clojure developer thrown into an “enterprise” Java/Spring/Groovy application, I have a unique opportunity to experience and think about the differences between functional (FP) and object-oriented programming (OOP) and approach to design. Today I want to compare how the solution would differ for a small subsystem responsible for checking for and progressing the process of fixing data discrepancies. The main question we will explore will be where do we deal with external effects, i.e. I/O.

“It will only take about an hour,” I said to her. Two days later, a pull request awaits review. Where has all that time gone? What are the sources of delay in software development and how can we make it faster?

When I came to the office one late autumn morning in 2005, I have been shocked to find out that - without any warning signs whatsoever - I hd been fired. That day I have learned the importance of communication. Their criticism was justified but the thing is, nobody bothered to tell me anything during my 11 months in the company. I received exactly 0 feedback about my behaviour or work. The company ended up at court with its client - which both explains why they were stressed and was also caused by bad communication. So communication - even, or especially under stress - is really important. It must be open, transparent, and broad.

The funny thing is that I still do the things they fired me for.