Haskell 用foldM和State编写一个简单函数

我试图编写一个小函数，它基本上遍历一系列问题，对于每个问题，提示符将等待用户的响应，如果答案正确，则在分数上加1，如果答案错误，则不做任何操作

我认为如果我只需要记录分数，使用foldM就足够了，但是我还想打印每个问题在列表中的位置，比如“问题1:”等等

使用状态单子有助于跟踪分数和位置吗？ 除此之外，我很想和国家队练习

以下是当前代码：

每个问题都是一个包含字符串和答案的元组

import Control.Monad
import Control.Concurrent
import System.Exit


qs =
    [( "question"
     ,["1"]            --number of the correct answer, from 1 to 4
    ]

main =
    putStrLn "Type \"init\" to begin" >>
    getLine >>= \l -> case l of
        "init" -> act
        _      -> main

act :: IO ()
act =
    let score = foldM (
        \acc (q,a) ->
        putStrLn q >>
        getLine >>= \l ->
        if (l `elem` a)
            then putStrLn "CORRECT!"    >>
                 threadDelay (2 * 10^6) >>
                 acc >>= \a -> a + 1
            else putStrLn "WRONG!"      >>
                 threadDelay (2 * 10^6) >>
                 acc
    ) 0 qs
    in  putStrLn $ "Score: " ++ score >>
    if (score > 18)
        then putStrLn "Bravo!"    >>
        else putStrLn "Not enough!" >>
    putStrLn "Type \"1\" to restart, anything else to quit" >>
    getLine >> \l -> case l of
        "1" -> act
        _   -> exitSuccess

---

如果您自己提取迭代函数，则可以简化事情：

import Control.Monad

go score (question,answer) = do
  putStr $ question ++ "? "
  response <- getLine
  if response /= answer
    then do putStrLn "Wrong!"
            return score
    else do putStrLn "Right!"
            return (score+1)

questions = [ ("1+1=", "2"), ("2+2","4"), ("What is your favorite color", "\n") ]

doit = foldM go 0 questions

import-Control.Monad
去得分（问题、答案）=去做
putStr$question++“？”
响应这里有一个示例，使用
StateT
来同时考虑
状态
和
IO

module Main where

import Control.Monad.State

type Question = (String,String)
type Questions = [Question]
type Score = Int
type Game = StateT Score IO ()  -- combine State and IO effects

play :: Question -> Game
play (question,answer) = do
  liftIO $ putStrLn question  -- IO requires using the liftIO function explicitly
  input <- liftIO $ getLine
  if answer == input
    then do
      liftIO $ putStrLn "correct!"
      modify (+1) -- add 1 to score
    else
      liftIO $ putStrLn "wrong!"
  score <- get
  liftIO $ putStrLn $ "Your score is: " ++ (show score)

questions :: Questions
questions = [("1+1=", "2"), ("What is the best programming language?", "haskell")]

main :: IO ()
main = do
  runStateT (traverse play questions) 0  -- no need for foldM since we're using State to handle the score
  putStrLn "game over"

modulemain其中
进口控制单体状态
类型问题=（字符串，字符串）
类型问题=[问题]
类型分数=整数
类型Game=StateT Score IO（）--组合状态和IO效果
游戏：问题->游戏
玩（问题，回答）=做
liftIO$putStrLn问题——IO需要显式使用liftIO函数
如果没有IO，您可以使用状态进行输入。作为练习，您可以将所有代码转换为纯代码，例如，通过提供一个答案列表来替换交互式getLine。如果您想使用State和IO，您需要使用StateT（monad转换器：我建议您先编写纯版本）。
module Main where

import Control.Monad.State

type Question = (String,String)
type Questions = [Question]
type Score = Int
type Game = StateT Score IO ()  -- combine State and IO effects

play :: Question -> Game
play (question,answer) = do
  liftIO $ putStrLn question  -- IO requires using the liftIO function explicitly
  input <- liftIO $ getLine
  if answer == input
    then do
      liftIO $ putStrLn "correct!"
      modify (+1) -- add 1 to score
    else
      liftIO $ putStrLn "wrong!"
  score <- get
  liftIO $ putStrLn $ "Your score is: " ++ (show score)

questions :: Questions
questions = [("1+1=", "2"), ("What is the best programming language?", "haskell")]

main :: IO ()
main = do
  runStateT (traverse play questions) 0  -- no need for foldM since we're using State to handle the score
  putStrLn "game over"