打印两个数字的总和Haskell

Question

如何打印两个数字之和的结果？

 main:: IO()
 main = do putStrLn "Insert the first value: "  
        one <- getLine  
        putStrLn "Insert the second value: "  
        two <- getLine    
        putStrLn "The result is:"
    print (one+two)

这给了我一个错误:

  ERROR file:.\IO.hs:3 - Type error in application
  *** Expression     : putStrLn "The result is:" print (one + two)
  *** Term           : putStrLn
  *** Type           : String -> IO ()
  *** Does not match : a -> b -> c -> d

Answer 1

尝试使用readLn而不是getLine.

getLineString在IOmonad中返回a 并且String无法添加s.

readLn具有多态返回类型,并且编译器推断返回类型是Integer(在IOmonad中),因此您可以添加它们.