Domain Modeling Made Functional

Monads and More

This book tries to avoid too much jargon, but one word that comes up all the time in functional programming is monad. So let’s pause and talk a little about monads now. The m-word has a reputation for being scary, but in fact we’ve already created and used one in this very chapter!

A monad is just a programming pattern that allows you to chain “monadic” functions together in series. OK, then what’s a “monadic” function? It’s a function that takes a “normal” value and returns some kind of “enhanced” value. In the error-handling approach developed in this chapter, the “enhanced” value is something wrapped in the Result type, so a monadic function is exactly the kind of Result-generating “switch” functions that we’ve been working ...