You still have to deal with the ugliness in a dynamic language too, but you might be tempted to just let duck typing do its thing, which could lead to disastrou

You still have to deal with the ugliness in a dynamic language too, but you might be tempted to just let duck typing do its thing, which could lead to disastrous results. Otherwise, you'll have to check types and invariants, at which point you might as well parse the input into type-safe containers.