Haskell:Turtle:命令行解析器

Question

我一直在尝试用 Turtle 构建一个命令行解析器，没什么花哨的:https://github.com/Tyrn/go-procr

#!/usr/bin/env stack
{-# LANGUAGE OverloadedStrings #-}

module Main where

import Turtle
import Prelude hiding (FilePath)

parserSwitch :: Parser (Bool, Bool)
parserSwitch = (,) <$> switch "verbose" 'v' "Unless verbose, just progress bar is shown"
                   <*> switch "filetitle" 'f' "Use file name for title tag"

parserArg :: Parser (FilePath, FilePath)
parserArg = (,)    <$> argPath "src" "Source directory"
                   <*> argPath "dst" "Destination directory"

main :: IO ()
main = do
  (verbose, filetitle) <- options "Flags" parserSwitch
  echo (format ("verbose: "%w) verbose)
  echo (format ("filetitle: "%w) filetitle)
  (src, dst) <- options "Args" parserArg
  echo (format ("src: "%fp) src)
  echo (format ("dst: "%fp) dst)

需要三种参数: bool 标志；选项、文本和整数；位置参数。到目前为止，我陷入了 bool 标志和位置参数的困境。不幸的是，即使如此，这些例子似乎也太基础了。

1. 我真的必须为不同类型的选项构建单独的解析器(我无法用单个解析器满足语法要求)吗？

2. 无论如何，它都不会按预期工作。

我不知道下一步应该做什么。

Answer 1

您的第一步是拥有可以轻松存储和检索选项的东西:

data Settings = Settings
   { settingsVerbose      :: Bool
   , settingsFileTitle    :: Bool
   , settingsSource       :: FilePath
   , settingsDestination  :: FilePath
   }

然后，您为您的选项编写解析器。为了让事情变得清楚，让我们先说得详细一些:

verboseParser :: Parser Bool
verboseParser = switch "verbose" 'v' "Be more verbose"

fileTitleParser :: Parser Bool
fileTitleParser = switch "filetitle" 'f' "..."

sourceParser :: Parser FilePath
sourceParser = argPath "src" "Source directory"

destinationParser :: Parser FilePath
destinationParser = argPath "dst" "Destination directory"

由于 Parser 是 Applicative 的实例，因此我们可以将所有选项组合在一个解析器中:

settingsParser :: Parser Settings
settingsParser = 
    Settings <$> verboseParser
             <*> fileTitleParser
             <*> sourceParser
             <*> destinationParser

我们将所有四个解析器组合成一个解析器，类似于通过 (,) 进行的组合。现在我们可以通过单次调用options来解析选项。毕竟，要么所有参数都是正确的，要么我们必须向用户展示正确的用法:

main = do
   s <- options "Description of your program" settingsParser

   echo (format ("verbose: "%w)   (settingsVerbose s))
   echo (format ("filetitle: "%w) (settingsFileTitle s))
   echo (format ("src: "%fp)      (settingsSource s))
   echo (format ("dst: "%fp)      (settingsDestination s))

不过，您可能想使用较短的名称，并且可能在 settingsParser 中编写解析器:

data Settings = Settings
   { sVerbose     :: Bool
   , sFileTitle   :: Bool
   , sSource      :: FilePath
   , sDestination :: FilePath
   }

settingsP :: Parser Settings
settingsP = 
  Settings <$> switch "verbose"   'v' "Be more verbose"
           <*> switch "filetitle" 'f' "..."
           <*> argPath "src" "Source directory"
           <*> argPath "dest" "Destination directory"

description :: Description
description = "Description of your program"

main = do
  (Settings verbose filetitle source dest) <- options description settingsP
  ...