Treat a --version flag specially

[parsonsmatt]

Currently, optparse-generic supports --help as a special case.

It'd be nice to also support --version as a special case. It's currently possible to support in a record argument like:

data Opts = Opts { version :: Bool } deriving (Generic, ParseRecord)

main = do
    Opts {..} <- getRecord "main"
    when version $ do
        print version
        exitSuccess
    do the rest of the stuff

This does not work with a subcommand parser. Or, it kinda does, but you need --version after selecting a sub-command. Or you make version it's own subcommand.

data Cmd = Version | OtherCommand
    deriving (Generic, ParseRecord)
    
main = do
    cmd <- getRecord "Cmd"
    case cmd of
        Version -> print version
        OtherCOmmand -> etc

This can be worked-around with a hack:

main = do
    args <- getArgs
    when ("--version" `elem` args) $ do
        print version >> exitSuccess
    Opts {..} <- getRecord "main"
    etc

But then we don't get pretty documentation on the --version flag.

okay, that's a lot of prelude,

Request

getRecordWithVersion 
    :: ParseRecord a
    => IO ()
    -- ^ Action to call if a `--version` flag is passed
    -> String
    -> IO a 

which augments the a parser with the --version flag and calls the special thing.

This would probably be pretty easy to support as an external library, or as app-local code.

[Gabriella439]

Yeah, I would accept a pull request to add this

[silky]

Just adding another vote for this :) Came to the issues looking to report just this!