Monad laws in Ruby

5 minute read

I’ve been using monads in Ruby since May 2016, but I haven’t really understood the theoretical basis for them. I thought about learning Haskell, but I gave up pretty soon: I didn’t think I would benefit from it. Moreover, we started using ReasonML in Planado, which improved my functional programming skills to the point I didn’t really need a new functional language in my life. Why bother with learning Haskell when you know Ruby and Reason, right?

In early 2018, I became curious about theoretical aspects of functional programming, especially the monad laws. That’s when I realized that I really needed Haskell, mainly because everyone used it in their articles. It was extremely annoying because I couldn’t even read the code. How was I going to apply those things in Ruby if I can’t even understand what they’re saying? So I got a little help.

I grabbed my laptop and a friend who knows Haskell and figured out how to describe the three monad laws using Ruby’s dry-monads gem.

Railway Oriented programming in Ruby: do notation vs dry-transaction

7 minute read

Railway oriented programming is a design pattern which helps us handle errors in our applications. Instead of relying on exceptions, we design our data and functions in a specific way. Since applications are essentially just a combination of steps, we’ll make some design decisions about those steps and their structure:

• There is a Result type, which can be either a Success or a Failure
• Success and Failure are practically containers with different data
• Steps accept Result and return Result
• Once a step returns Failure, we stop further execution

I want to emphasize that Result is just an alternative name for the Either monad. Railway Oriented Programming comes from functional programming, so it is tightly related to the usual FP concepts like monads, composition, and many others. However, you don’t need to have an extensive knowledge of monads to use ROP in your code. In this article, I’ll show you how to write railway-oriented code in Ruby.