Resolução da lista de interatividade

Lib.hs

module Lib
    ( someFunc, getLine', putStr', putStrLn', putStr'', acumular, somador, somador2, obterLinha
    ) where

import Text.Printf
import System.IO

someFunc :: IO ()
someFunc = putStrLn "someFunc"


getLine' :: IO String
getLine' = do x <- getChar
              if x == '\n' then
                 return []
              else
                 do xs <- getLine'
                    return (x:xs)

putStr' :: String -> IO ()
putStr' [] = return ()
putStr' (x:xs) = do putChar x
                    putStr' xs


putStrLn' :: String -> IO ()
putStrLn' [] = return ()
putStrLn' s = do putStr' s
                 putChar '\n'


putStr'' :: String -> IO ()
putStr'' [] = return ()
putStr'' s = sequence_ [putChar c | c <- s]

somador :: IO ()
somador = do putStr "Quantos números? "
             n <- readLn :: IO Int
             soma <- acumular n 0
             putStr $ printf "O total é %d" soma

acumular :: Int -> Int -> IO Int
acumular 0 acc = return acc
acumular n acc = do x <- readLn :: IO Int
                    acumular (n - 1) (x + acc)

somador2 :: IO ()
somador2 = do putStr "Quantos números? "
              n <- readLn :: IO Int
              ns <- sequence [readLn :: IO Int | _ <- [1 .. n]]
              putStr $ show $ sum ns

obterChar:: IO Char
obterChar = do hSetEcho stdin False
               x <- getChar
               hSetEcho stdin True
               return x

obterLinha :: IO String
obterLinha = do x <- obterChar
                if x == '\n' then
                    do putChar x
                       return []
                else
                    if x == '\DEL' then
                        do putStr "\b \b"
                           return "\DEL"
                    else
                        do putChar x
                           xs <- obterLinha
                           if xs == "\DEL" then
                              do obterLinha
                           else
                              return (x:xs)