Now that we have the basics of our architecture in place we can start to explore things to do with it that unlock capabilities that were not even possible in the old way of making the app. There is a concept that we have discussed a number of times on Point-Free known as “higher-order constructions.” This is where you take some construction that you have been studying and lift it to a higher-order by considering functions that take that object as input and return that object as output. The canonical example is “higher-order functions”, which are functions that take functions as input and return functions as output.

But on Point-Free we’ve also considered “higher-order random number generators”, which were functions that took our Gen type as input and returned the Gen type as output. And we’ve considered “higher-order parsers”, which are functions that take parsers as input and return parsers as output. Each time you form one of these higher-order constructions you gain the ability to unlock something new that the vanilla constructions could not do alone.