Filtering composite structures with Lens

Question

I have a [(a, Maybe b)], and want to obtain a [(a, b)], with all pairs where the second element was Nothing filtered out. Is there a concise way to describe this operation using lens?

Answer 1

How about something like

[('a',Just 1),('b',Nothing)]^..folded.aside _Just 

Using (^..) and folded from Control.Lens.Fold and aside and _Just from Control.Lens.Prism.

The key is aside, a handy function that builds a prism working on a pair from a prism working on a component of the pair.