Hot take: the NonEmpty list type is less useful than it seems. Because when we need to filter we're back to a list and many functions take lists/return lists. On the other hand the implicit order of elements in a list can be much more interesting to model (see Data.List.Ordered)
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You are correct about filter.. Evidence: filtered is not a valid Traversal (bits missing to get to here). There are vast number of other useful operations though, and I bet they are hidden in your code! Consider: (Apply f, Profunctor p) => (p a (f b)) -> p s (f t)
PS: I realised how difficult this line of reasoning is to explain on twitter as I was typing, so please accept my my "bits missing"
