Any sufficiently polymorphic strongly typed language is indistinguishable from Javascript
Ehh, that's a bit overblown. In particular, even if you actually did make the weird list-number, you'd end up with a type error as soon as you tried to use it somewhere expecting a regular number.
Just implement `Num a => Num [a]`, easy.
That would let you make the instance only be a little bit unlawful instead of totally unlawful, but I don't see how it would affect the type errors you'd get.