Created
July 30, 2020 08:52
-
-
Save sordina/786161fd6565557eae7fb161d70a1218 to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
{-# LANGUAGE DeriveFunctor #-} | |
module Main where | |
-- see https://jtobin.io/sorting-with-style | |
import Control.Arrow ((***)) | |
import Data.Function ((&)) | |
import Data.Functor.Foldable (hylo) | |
import Data.List.Ordered (merge) | |
-- Testing! | |
main :: IO () | |
main = do | |
print $ mergesort $ reverse $ [1..10] ++ [2..13] | |
print $ mergesort' $ reverse $ [1..10] ++ [2..13] | |
-- Implementation 1 | |
mergesort :: Ord a => [a] -> [a] | |
mergesort [] = [] | |
mergesort [a] = [a] | |
mergesort as = as & merge' . (mergesort *** mergesort) . partition | |
merge' :: Ord a => ([a], [a]) -> [a] | |
merge' (as, []) = as | |
merge' ([], bs) = bs | |
merge' (as@(a:as'), bs@(b:bs')) | |
| a <= b = a : merge' (as', bs) | |
| otherwise = b : merge' (as, bs') | |
partition :: [a] -> ([a], [a]) | |
partition xs = go ([],[]) xs | |
where | |
go p [] = p | |
go (l,r) (a:as) = go (r, a:l) as | |
-- Implementation 2 | |
mergesort' :: Ord a => [a] -> [a] | |
mergesort' = hylo folder unfolder | |
data Tree a r = Empty | |
| Leaf a | |
| Branch (r, r) | |
deriving Functor | |
unfolder :: [a] -> Tree a [a] | |
unfolder [] = Empty | |
unfolder [x] = Leaf x | |
unfolder xs = Branch (partition xs) | |
folder :: Ord a => Tree a [a] -> [a] | |
folder Empty = [] | |
folder (Leaf x) = [x] | |
folder (Branch (l,r)) = merge l r |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment