Haskell你好世界不会编译

Question

这段代码有什么问题？试图做一个基本的haskell你好世界.

module Main
( hello )
where

hello :: [Char] -> [Char]
hello p = "Hello " ++ p ++ "!"

main =
  let msg = hello "World"
  putStrLn msg

Answer 1

你错过了一个do:

main = do
  let msg = hello "World"
  putStrLn msg

您还需要导出main:

module Main ( main ) where

由于这是主要模块,因此无需导出hello.

Answer 2

你错过了一个in:

main = let msg = hello "World" in putStrLn msg