repMax.hs

{-# LANGUAGE RecursiveDo #-}

import qualified Data.Map.Strict as Map
import Control.Monad.State.Strict

repMax :: (Traversable t, Ord a) => t a -> t a
repMax xs = flip evalState Nothing $ mdo
  ys <- forM xs $ \x -> do
    modify (max (Just x))
    pure (max x res)
  ~(Just res) <- get
  pure ys