loop example.hs

import Control.Arrow (loop)

replaceWithMax, replaceWithMax' :: Ord a => [a] -> [a]

replaceWithMax xs =
  let (result, max) = go (xs, max)
   in result
  where
    go ([], replacer) = ([], replacer)
    go ([x], replacer) = ([replacer], x)
    go ((x:xs), replacer) =
      let (xs', replacer') = go (xs, replacer)
       in (replacer : xs', max replacer' x)

replaceWithMax' = loop go
  where
    go ([], replacer) = ([], replacer)
    go ([x], replacer) = ([replacer], x)
    go ((x:xs), replacer) =
      let (xs', replacer') = go (xs, replacer)
       in (replacer : xs', max replacer' x)