Init and Last

init-last.hs

import           Data.Bifunctor (first)
import           Data.List      (foldl')

type Diff a = [a] -> [a]

match :: [a] -> Either () ([a], a)
match = (fmap . first) ($[])    -- extract the Diff list
      . foldl' go (Left ())
  where
    go  :: Either () (Diff a, a)
        -> a
        -> Either () (Diff a, a)
    go (Left  _      ) x = Right (id       , x)
    go (Right (ys, y)) x = Right (ys . (y:), x)