Nobody writes dynamically typed functions that can be called with any possible type.
replyIt's not about that at all. Static types give you errors reliably at compile time instead of randomly at runtime, better documentation of what the code expects (people writing dynamically typed languages eventually resort to type comments), working IDE support, reliable refactoring and better code, all of which results in faster development.
The cost is a more complex language, occasionally difficult-to-write types, and very occasionally impossible-to-write types. But those are very very minor in comparison to the pros.
> (people writing dynamically typed languages eventually resort to type comments)
replyThis has never been an issue in Elixir, because instead of a comment, you'd just improve the pattern matching in the function definition.
def blah(%{students: [%{firstname: firstname, lastname: lastname}|[]], count: cnt}) when is_int(cnt):
fullname = firstname <> lastname