Well written typespecs + dialyzer catches most things you’d want to catch with a type system: https://hexdocs.pm/elixir/typespecs.html

There is also pattern matching and guard clauses so you can write something like:

def add(a, b) when is_integer(a) and is_integer(b), do: a + b

def add(_, _), do: :error

It’s up to personal preference and the exact context if you want a fall through case like this. Could also have it raise an error if that is preferred. Not including the fallback case will cause an error if the conditions aren’t met for values passed to the function.