用ghci记录历史 [英] Keeping track of history in ghci

问题描述

历史管理如何在GHCI或其他基于Haskell的REPL中工作？由于Haskell是一种纯粹的语言，我想它是用monad实现的，也许是 state monad 。请注意，我是Haskell的初学者，所以请提供详细的解释，而不仅仅是链接到源代码。

$ b
$ b $ b

解决方案

这是程序如何保存用户输入的命令历史的简单示例。它基本上和数字猜测游戏具有相同的结构，所以一旦你明白你应该没有理解这一点：

  import Control.Monad.State 
 import Control.Monad 
 $ b $ shell :: StateT [String] IO（）
 shell = forever $ do 
 lift $ putStr$ 
 cmd<  -  lift getLine 
 if cmd ==history
然后执行hist<  -  get 
 lift $ forM_ hist $ putStrLn 
 else modify（+ + [cmd]）
 
 main = do putStrLn欢迎使用history shell。 
 putStrLn输入'history'查看您的命令历史记录。 
 execStateT shell [] 
  

How does history management work in GHCI or other Haskell-based REPLs? Since Haskell is a pure language, I guess it's implemented using a monad, perhaps the state monad.

Kindly note I'm a beginner in Haskell, so please provide a detailed explanation rather than just linking to the source.

解决方案

This is a simplified example of how a program might keep a history of commands entered by the user. It basically has the same structure as the number guessing game, so once you understand that you should have no trouble understanding this:

import Control.Monad.State
import Control.Monad

shell :: StateT [String] IO ()
shell = forever $ do
  lift $ putStr "$ "
  cmd <- lift getLine
  if cmd == "history"
    then do hist <- get
            lift $ forM_ hist $ putStrLn
    else modify (++ [cmd])

main = do putStrLn "Welcome to the history shell."
          putStrLn "Type 'history' to see your command history."
          execStateT shell []

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