optparse-applicative的(Sub)命令同义词

data Sub a = Sub
  { subparser :: Parser a
  , subname   :: Text
  , subdesc   :: Text
  }

{-# LANGUAGE OverloadedStrings #-}

import Options.Applicative
import Data.Text (Text)

data Command = Commit Text
             | Push Text
             | Pull Text

commitParser :: Parser Command
commitParser = Commit <$> strOption
  ( long "message"
  <> short 'm'
  <> metavar "MESSAGE"
  <> help "Commit message" )

pushParser :: Parser Command
pushParser = Push <$> strOption
  ( long "remote"
  <> short 'r'
  <> metavar "REMOTE"
  <> help "Remote repository" )

pullParser :: Parser Command
pullParser = Pull <$> strOption
  ( long "branch"
  <> short 'b'
  <> metavar "BRANCH"
  <> help "Branch to pull" )

subcommands :: Parser (Sub Command)
subcommands = subparser
  ( command "commit" (info commitParser (progDesc "Commit changes"))
    <> command "push" (info pushParser (progDesc "Push changes to remote"))
    <> command "pull" (info pullParser (progDesc "Pull changes from remote")) )

main :: IO ()
main = execParser (info (helper <*> subcommands) fullDesc) >>= print

mainParser :: Parser Command
mainParser = subcommands <|> pure (Commit "default message")

main :: IO ()
main = execParser (info (helper <*> mainParser) fullDesc) >>= print

./your-app commit -m "Your commit message"