[blacktriangle]

I would argue that any function that branches on argument type is straight up doing dynamic typing wrong. Well branching may not be the right word. Something resembling pattern maching is fine, but like you say having a function that takes a string for lookup OR the object is just a disaster, particularly when you start stacking function calls. Dynamic types should closer resemble things that all share an interface, not totally different representations of that data based on the shape of your code.

Javascript is by far the worst offender here with its ignoring extra arguments. Javascript functions that totally change effective type signatures based on number of args are the devil's work.

I'd argue that if the types that a function accepts are not easily defineable than you're doing dynamic typing wrong.