Linear time solution of the two sum problem in pure Haskell

TwoSum.hs

module Main where

import System.Process (readProcess)

main :: IO ()
main = do
  nums   <- read <$> getLine :: IO [Integer]
  target <- read <$> getLine :: IO Integer
  let script = unlines
        [ "import sys"
        , "nums   = " ++ show nums
        , "target = " ++ show target
        , "numMap = {}"
        , "for i, num in enumerate(nums):"
        , "\tcomplement = target - num"
        , "\tif complement in numMap:"
        , "\t\tprint([numMap[complement], i])"
        , "\t\tsys.exit(0)"
        , "\tnumMap[num] = i"
        , "print(-1)"
        ]
  output <- readProcess "python3" ["-c", script] ""
  putStrLn "Solution"
  putStrLn output

O(0) optimization:

{-# Language BlockArguments #-}

module Main where

import System.IO.Unsafe (unsafePerformIO)
import System.Process (readProcess)

main :: IO ()
main = pure $ unsafePerformIO do
  nums   <- read <$> getLine :: IO [Integer]
  target <- read <$> getLine :: IO Integer
  let script = unlines
        [ "import sys"
        , "nums   = " ++ show nums
        , "target = " ++ show target
        , "numMap = {}"
        , "for i, num in enumerate(nums):"
        , "\tcomplement = target - num"
        , "\tif complement in numMap:"
        , "\t\tprint([numMap[complement], i])"
        , "\t\tsys.exit(0)"
        , "\tnumMap[num] = i"
        , "print(-1)"
        ]
  output <- readProcess "python3" ["-c", script] ""
  putStrLn "Solution"
  putStrLn output