Tagless Final is a popular pattern of advanced functional programming that can be used to abstract away capabilities and side effects you do not know ahead of time and cannot predict. As usual, the best way to see how it works and why it is useful is to look at some examples.
Tagless Final
Programming to capabilities
Imagine you are writing an application that is to be executed against more than one environment. Such scenarios are common in the real world. A good example is mobile applications. You can have multiple mobile platforms. However, you would like to publish your applications to all of them. The platforms that exist are quite different from each another. And usually, it is pretty tedious to reimplement your application...