I believe you’re misunderstanding the intent of that paragraph. It is correct that errors are not used as control flow, and that’s why the function explicitly says “must be the string representation of an integer”. The paragraph supports this, you shouldn’t wrap String.to_integer in a try. That’s the intent of the paragraph, not that errors are not used at all. Rather they should be used for “unexpected and/or exceptional situations”, such as someone passing "hello" to String.to_integer. Just like it should raise if it is passed :potato.
Elixir consistently raises ArgumentError for invalid inputs in the cases where the input doesn’t make sense at all.
Another great example of this is of course Integer.parse, which accepts any string, because it’s made specifically for unknown string inputs, while it throws an ArgumentError if the base is incorrect.
Digging deeper into the Elixir source can be helpful here, where you’ll find lots of instances of raising ArgumentError (there are also other errors used regularly, like KeyError)
