Question

主要功能：

main = do
  x <- getLine
  lines <- replicateM x getLine
  print $ lines

我得到的错误：

Couldn't match type `[Char]' with `Int'
Expected type: Int
  Actual type: String
In the first argument of `replicateM', namely `x'
In a stmt of a 'do' block: lines <- replicateM x getLine

需要一种方法来解决这个问题。

Answer 1

replicateM就像replicateM :: Monad m => Int -> m a -> m [a] 作为getLine :: IO String的地方＆＃34; X＆＃34;需要Int但getLine返回IO String，你可以read x :: Int：

main = do
  x <- getLine
  lines <- replicateM (read x :: Int) getLine
  print $ lines

或只是做：

main = do
  x <- readLn
  lines <- replicateM x getLine
  print $ lines

readLn可能会x作为IO Int

从文件获取输入时出错

1 个答案: