Monad examples

This repository contains the example code used for the talk "Monads for the working software engineer" I gave at QAware Engineering Camp 2020.

It consists of three parts:

• A simple piece of baseline code that implements a simple calculator function

• Three different extensions of the baseline code in different directions:

  • Possibility of null return value

  • Multiple results (as a Set)

  • State (in this case, a counter)

• A presentation of the same extensions in "monadic form", that is, with the help of two functions just and bind. While these functions are implemented differently in each case, the main evaluation function is identical, since all all the plumbing is now part of the helper functions. These functions constitute the monad abstraction.

• As an addition, we also give an implementation of the combined monad (state and set), which still allows expressing the calculator in the same way.

Furthermore, Fabian Huch contributed a Scala version of some of the material, which can also be found here. Unlike Kotlin, Scala allows us to define the Monad structure as a general (higher-kinded) trait, instead of just a pattern.

Enjoy!