Proposal: add unfoldr1 to the somewhere in base

Way back in 2001, Shin-Cheng Mu proposed an unfoldr1 combinator: http://code.haskell.org/~dons/haskell-1990-2000/msg06775.html I discussed this a bit with shachaf in #haskell, and he noted that a similar function, with a slightly different but isomorphic type, appears in Edward Kmett's semigroups package as the unfoldr for NonEmpty. I propose that we add this. It can be written unfoldr1 :: (b -> (a, Maybe b)) -> b -> [a] unfoldr1 f b = go b where go b = case f b of (a, may_b) -> a : maybe [] go may_b With the appropriate RULES, it can be wrapped up in build and fuse properly. I'd love to see this written as an unfoldr instead. Does anyone know if that's possible?