Quick Sort in Haskell

Welcome to the Quick Sort in Haskell page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

module Main where

import Text.Read
import System.Environment
import System.Exit (exitWith, ExitCode(ExitFailure))
import Data.List (intercalate)


quickSort :: Ord a => [a] -> [a]
quickSort []     = []
quickSort (x:xs) =
  let left  = quickSort $ filter (<= x) xs
      right = quickSort $ filter (> x)  xs
  in left ++ [x] ++ right


headMaybe :: [a] -> Maybe a
headMaybe []     = Nothing
headMaybe (x:xs) = Just x

-- Converts string in format "1, 2, 3" to a Maybe list of int
stringToListMaybe :: String -> Maybe [Int]
stringToListMaybe str = readMaybe $ "[" ++ str ++ "]" :: Maybe [Int]

-- Ensure that a list contains at least two elements
verifyListLength :: Ord a => [a] -> Maybe [a]
verifyListLength []     = Nothing
verifyListLength [x]    = Nothing
verifyListLength (x:xs) = Just (x:xs)

listToString :: [Int] -> String
listToString = intercalate ", " . map show


main :: IO ()
main = do
  args <- getArgs
  let xs = headMaybe args >>= stringToListMaybe >>= verifyListLength
  case xs of
    Nothing -> do
      putStrLn "Usage: please provide a list of at least two integers to sort in the format \"1, 2, 3, 4, 5\""
      exitWith $ ExitFailure 1
    Just xs  -> putStrLn $ listToString $ quickSort xs

Quick Sort in Haskell was written by:

• Parker Johansen

If you see anything you'd like to change or update, please consider contributing.

Note: The solution shown above is the current solution in the Sample Programs repository as of Mar 26 2019 01:28:05. The solution was first committed on Dec 04 2018 20:35:19. As a result, documentation below may be outdated.

How to Implement the Solution

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How to Run the Solution

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