如何用optparse-appative来解析

本文介绍了如何用optparse-appative来解析的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我正尝试使用来解析 a>：

See the following passage of the code> Combinator in Control.Applicative ：

optional $ strOption
   ( long "output"
  <> metavar "DIRECTORY" )

因此，您只需将可选的组合子应用于 strOption $ b

Accordingly, all you have to do is apply the optional combinator to the result of strOption:

import Options.Applicative

data Config = Config
    { cIn  :: Maybe String
    , cOut :: Maybe String
    } deriving Show

configParser :: Parser Config
configParser = Config
    <$> (optional $ strOption $ long "in" <> short 'i')
    <*> (optional $ strOption $ long "out" <> short 'o')

main :: IO ()
main = do
    conf <- execParser (info configParser fullDesc)
    print conf

命令行测试：

$ main --in foo -o bar
Config {cIn = Just "foo", cOut = Just "bar"}
$ main -i foo
Config {cIn = Just "foo", cOut = Nothing}

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