haskell - 保留算法不正常

Question

运行这段代码的输出是不正确的，我不能悲伤地抱住头，不知道我自己的代码哪里错了。我盯着它看了好几个小时。

代码:

import System.IO(isEOF)

reverseIO :: IO ()
reverseIO = do 
  line <- getLine
  done <- isEOF
  if null line
    then return ()
  else if done then
    putStrLn $ reverseStr line
  else do
      reverseIO

reverseStr :: [w] -> [w]
reverseStr [] = []
reverseStr (x:xs) = reverseStr xs ++ [x]

main = do
  reverseIO

期望:<强>2。反转并打印出来。

> hello world
world hello

运行:

GHCi, version 8.10.6: https://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/runner/University-Labs/.ghci
[1 of 1] Compiling Main             ( Main.hs, interpreted )
Ok, one module loaded.
 hello world

编辑:按Ctrl+D，

GHCi, version 8.10.6: https://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/runner/University-Labs/.ghci
> hello world
dlrow olleh

Answer 1

您必须将 replaceStr 替换为 unwords 。撤销 。单词:

reverseIO = do 
  line <- getLine
  done <- isEOF
  if null line
    then return ()
  else if done then
    putStrLn . unwords . reverse . words $ line
  else reverseIO