Why Algebraic Effects?

Summary

Why Algebraic Effects Algebraic effects (a.k.a. effect handlers) are a very useful up-and-coming feature that I personally think will see a huge surge in popularity in the programming languages of tomorrow. They’re one of the core features of Ante, as well as being the focus of many research languages including Koka, Effekt, Eff, and Flix. However, while many articles or documentation snippets try to explain what effect handlers are (including Ante’s own documentation), few really go in-depth on why you would want to use them. In this post I’ll explain exactly that and will include as complete a list as possible on all the use-cases of algebraic effects. A Note on Syntax and Semantics I’ll be using Ante pseudocode for much of this article. If you’re not familiar with effect handlers or Ante I encourage you to read the documentation link above or read from any of the other effectful languages for a good head start! But I recognize it’s hard to get buy-in to learn something before showing why it is useful first (hence this blog post!). So I’ll give a quick elevator pitch on a good mental model to think about effects. You can think of algebraic effects essentially as exceptions that you can resume. You can declare an effect function: effect SayMessage with // This effect function takes a Unit type and returns a Unit type. // Note that `Unit` is roughly the same as `void` in imperative languages. // There are differences between them but none that are relevant here. say_message: Unit -> Unit You can “throw” an effect by calling the function, and the function you’re in must declare it can use that effect similar to checked exceptions: foo () can SayMessage = say_message () 42 And you can “catch” effects with a handle expression (think of these as try/catch expressions): handle foo () | say_message () -> print "Hello World!" // print out Hello World! resume () // then resume the computation, returning 42 If you have further questions I again encourage you to read some doc...