I prefer code to be as assertive as possible about structure and constants if possible. If something in the function itself makes the assumption that lists are passed in
Well the thing is there’s no value in doing this redundantly. Repo.delete_all already checks that the inputs make sense. In fact the whole function is pretty redundant because Repo.delete_all is smart enough to no-op an empty list.
In this case it might be redundant, yeah, but in the general case you’ll get better error messages if you force structural matching when appropriate, because you’ll get errors about no function clause matching, which is generally super easy to debug. It’ll force the error earlier and be less messy.
I would add that I don’t think there is any downside to being as assertive as possible anywhere.
Here is my take:
def delete_db([]) do
:ok
end
def delete_db(values) do
Repo.delete_all(values)
end
Is really Enum.any? a replacement of length?
The documentation says:
Invokes the given fun for each item in the enumerable. It stops the iteration at the first invocation that returns a truthy value. Returns true if at least one invocation returns a truthy value. Otherwise returns false.
When I read this, I would expect that values would contain true/false values and as long as one of them is true… delete from the repo? I would flag this as a code smell, no?
Enum.any?/2 might gain you a bit, but only a little. For an empty list it returns always false, so you could do Enum.any?(list, &(&1)), which will return true for any non-empty list that does not consists of only nils and falses. But if you expect to have a list that might consit only of those, you can extend the filter: Enum.any?(list, &(&1 or (&1 == false) or (&1 == nil))) (untested).
But to be honest, I’d prefer to use Enum.empty?/1, but only if you can’t use a pattern match.
Was hoping somebody had posted this method - too often the beauty of pattern matching in function heads is forgotten! 
This topic made me realize that I need to work more on retraining my mind to see multiple function clauses not as overloaded functions but as distinct parts of one single function.
Edit: Sorry meant to be a general remark, not a specific reply.