Post #2735415

@byorgey@mathstodon.xyz @oantolin@mathstodon.xyz @das_g@chaos.social In fact, this recursion is a `concat` after an unfold. So it's also a list futumorphism: ``` futu :: (b -> Maybe ([a],b)) -> b -> [a] futu g z = case g z of Nothing -> [] Just (ys, z') -> ys ++ futu g z' ``` (Not stated is the requirement that the generated chunk `ys` should be nonempty, in order to guarantee progress. Alternatively one can make the body return `Maybe (a,[a],b)`, enforcing the requirement structurally.) Then we have: ``` conjugate :: [Int] -> [Int] conjugate = futu strip where strip [] = Nothing strip ns = Just (replicate m (length ns), takeWhile (>0) [ n - m | n <- ns ]) where m = minimum ns ```