Mastering Kotlin

Effects

Effects are abstractions that help us to encapsulate non-deterministic operations such as network requests or disk I/O. These types of operations don't fit as nicely into the pure mathematical model of functional programming because they take time, and their result is non-deterministic.

Arrow provides several abstractions with which we can model our side effect code:

• IO: A common data type for working with external systems such as networks or databases
• Async: A typeclass that represents asynchronous code with a callback
• Promise: Represents an asynchronous operation whose result is returned as a promise

Using IO, we can define a long-running operation and then consume it using typeclasses such as attempt() or runAsync():

IO<Int> ...