I noticed that your blog post differed from the actual code in your git repository. In the blog post, you defined `shift` to be:

   shift v = pad
     (map Just (concatMap add (group (catMaybes v)))))
     Nothing
     (length v)

whereas the code gives:

   shift v = take n (v' <> empty n)
     where
       n = length v
       v' = group (filter isJust v) >>= go
       go (Just a : Just b : ts) = Just (a + b) : go ts
       go ts = ts

From my understanding of the blog post's logic, the former doesn't handle the case where `v = replicate 4 (Just 2)`, since it returns `[Just 4, Just 2, Just 2, Nothing]`. Am I correct, and if so, why does the latter version fix this problem? For reference, I know little to no Haskell.