gistfile1.hs

import Data.List

mylst = [(1,3), (2,4), (5,6), (5,7), (6,8)]

findOverlaps :: [(Int,Int)] -> [(Int,Int)]
findOverlaps xs =
  let sorted = sortBy (\x y -> if ((fst x) < (fst y)) then LT else GT) xs
      foldF acum elem =
        let (doneLst, (blockMin,blockMax)) = acum
            (elemMin, elemMax) = elem
        in if elemMin > blockMax then
            ((blockMin,blockMax) : doneLst, elem)
          else
            (doneLst, (blockMin,elemMax))
      folded = foldl' foldF ([], head sorted) $ tail sorted
  in reverse $ snd folded : fst folded

main = do
  putStrLn $ show $ findOverlaps mylst