https://stackoverflow.com/questions/40755506

merge-dups.hs

#!/usr/bin/env stack
-- stack --resolver lts-7.8 --install-ghc runghc --package protolude

{-# LANGUAGE NoImplicitPrelude #-}

import Protolude

merge :: (Eq a, Semigroup a) => [a] -> [a]
merge (x:y:more) | x == y = (x <> y) : more
merge (x:xs) = x : merge xs
merge xs = xs

fix' :: (Eq a) => (a -> a) -> a -> a
fix' f x = if f x == x then x else fix' f (f x)

main :: IO ()
main = putStrLn $ (show $ getSum <$> fix' merge (Sum <$> [1, 1, 1, 1, 3, 2, 2, 4, 3]) :: Text)