Code Reuse Is a Big Value of Functional Programming

In typical OO, there's really only one thing you can express is I have these methods. And the methods are specific to that particular data structure attached to it. That kind of dance doesn't really exist in Haskell because it gets implemented by the library author once if they even need to care. But ask what gives you a lot of stuff for free as a user, as a library author, and sooner or later in your own project,. You're both because you're writing functions that you're calling.