Haskell中的简单文本菜单 [英] Simple text menu in Haskell

问题描述

我想知道什么是使用下面描述的功能创建简单菜单的最佳解决方案（伪代码），就像我习惯的那样：

  while（true）{
x = readLine（）; 
 case（x）：
x ==1然后做sth1函数
x ==2然后做sth2函数
} 
  
 
 
 
或者也许有关于如何制作不在上述模式中的菜单的任何其他想法？ 
 
 
 
 
  menu :: IO（）
 menu =做
 putStrLn。 unlines $ map concatNums options 
 choice<  -  getLine 
 case valid validate choice of 
 Just n  - >执行 。阅读$ choice 
 Nothing  - > putStrLn请再试一次
 
 menu 
 concatNums（i，（s，_））= show i ++）++ s 
 
 validate :: String  - >也许Int 
 validate s = isValid（读取s）
其中isValid [] = Nothing 
 isValid（（n，_）：_）
 | outOfBounds n = Nothing 
 |否则=只是n 
 outOfBounds n =（n <1）|| （n>长度选择）
 
 choices :: [（Int，（String，IO（）））] 
 choices = zip [1 ..] [
（ DoSomething，foo）
，（Quit，bar）
] 
 
 execute :: Int  - > IO（）
执行n = doExec $ filter（\（i，_） - > i == n）options 
其中doExec（（_，（_，f））：_）= f 
 
 foo = undefined 
 bar =未定义
  
您可以可能会将枚举拆分为选项，因此只有它的描述和函数，有点分离，但这是有效的。评估菜单功能可以让你选择做什么！
 
I would like to know what is the best solution to create simple menu with functionality described below (pseudo code) just like I'm used to:
while (true) {
    x = readLine();
    case (x):
         x == "1" then do sth1 function
         x == "2" then do sth2 function
}
Or maybe any other ideas on how to make a menu not in the pattern described above?
解决方案
Something like
menu :: IO ()
menu = do
      putStrLn . unlines $ map concatNums choices
      choice <- getLine
      case validate choice of
         Just n  -> execute . read $ choice
         Nothing -> putStrLn "Please try again"

      menu
   where concatNums (i, (s, _)) = show i ++ ".) " ++ s

validate :: String -> Maybe Int
validate s = isValid (reads s)
   where isValid []            = Nothing
         isValid ((n, _):_) 
               | outOfBounds n = Nothing
               | otherwise     = Just n
         outOfBounds n = (n < 1) || (n > length choices)

choices :: [(Int, (String, IO ()))]
choices = zip [1.. ] [
   ("DoSomething", foo)
 , ("Quit", bar)
 ]

execute :: Int -> IO ()
execute n = doExec $ filter (\(i, _) -> i == n) choices
   where doExec ((_, (_,f)):_) = f

foo = undefined
bar = undefined
You could probably split the enumerating in "choices" so you only have the descriptions and functions inside it, a little bit of separation, but this works. Evaluating the "menu" function will let you choose what to do!

                        
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