optparse-example.hs

import Options.Applicative

data Options = Options {
  optTimeout :: Maybe Int,
  optCommand :: Command }
  deriving Show

data Command
  -- domains
  = ListDomains (Maybe Int)
  | CreateDomain String
  | GetDomain String
  -- zones
  | ListZones (Maybe Int)
  | GetZone String
  deriving Show

main :: IO ()
main = customExecParser (prefs showHelpOnError) parser >>= print

parser :: ParserInfo Options
parser = info (helper <*> parseOptions) $
  mconcat [
    fullDesc,
    progDesc "X-program",
    header "x 0.0.1" ]

parseOptions :: Parser Options
parseOptions = Options
  <$> timeoutOpt
  <*> parseCommand
  where
    timeoutOpt = optional $ option auto $
      long "timeout" <> short 't' <> metavar "INT" <>
      help "specify a timeout for the query"

parseCommand :: Parser Command
parseCommand = subparser (domains <> zones)
  where
    domains = mkcmd "domains" "this does domain stuff" $
      subparser $ mconcat [
        mkcmd "list" "this lists" (ListDomains <$> limitOpt),
        mkcmd "create" "this creates" (CreateDomain <$> domainArg),
        mkcmd "get" "this gets" (GetDomain <$> domainArg) ]
    zones = mkcmd "zones" "this does zones stuff" $
      subparser $ mconcat [
        mkcmd "list" "this lists" (ListZones <$> limitOpt),
        mkcmd "get" "this gets" (GetZone <$> zoneArg) ]
    limitOpt = optional $ option auto $
      long "limit" <> short 'l' <> metavar "INT" <>
      help "limit the number of printed results"

-- Domain list|create <domain>|get <domain>|delete <domain>
-- Zones list|get <zone>

      
mkcmd :: String -> String -> Parser a -> Mod CommandFields a
mkcmd cmd desc parser =
  command cmd $ info (helper <*> parser) $ progDesc desc

domainArg :: Parser String
domainArg = strArgument (metavar "DOMAIN")

zoneArg :: Parser String
zoneArg = strArgument (metavar "ZONE")