Function spread_needs_a_sequence 

pub fn spread_needs_a_sequence(span: Span) -> RuntimeError

What a ... argument that is neither an Array nor a Vector is refused with.

A spread passes an existing sequence where a variadic parameter’s elements would go, so the two sequences are what it reads; bind_params reports anything else, and the linear-memory backend reports it from the instruction that does the appending. One wording, because it is one failure.