Monoid is a type class, similar to interfaces in Java, and this is what it makes easy: if your code uses the monoid interface of some type then you can swap the

Monoid is a type class, similar to interfaces in Java, and this is what it makes easy: if your code uses the monoid interface of some type then you can swap the underlying concrete type without changing your code, and it still works. Obviously, you can do that in any untyped language, too, but explicitly defining these contracts makes code easy to manage and understand. And the compiler will tell you if/how you're doing something wrong.