I think they mean you never write types for your variables or functions. They don't mean you can't create types. That's the reference to Hindley–Milner type sys

I think they mean you never write types for your variables or functions. They don't mean you can't create types. That's the reference to Hindley–Milner type system and type inference. You don't have to say x : Nat x = 5 You just say x = 5 I personally don't like that you don't seem to be able to manually describe the type for a fn/var, because it's very useful when prototyping to write stubs where you provide the typedef but then the actual variable/function is just marked as "todo"