Cloudy.Cli.Utils

Documentation

maybeOpt :: Show a => String -> a -> (Mod f a -> Parser a) -> Mod f a -> Parser (Maybe a)

This lifts a option Parser to a Parser of Maybe, allowing you to specify a default value.

Given a call like:

  maybeOpt "Which foobar to use" "bazqux" strOption (short 'f' <> metavar "FOOBAR") :: Parser (Maybe Text)

this returns Nothing if the user doesn't specify the -f option, and Just if the user does. It also shows that the default values is "bazqux".

Using maybeOpt is different than just using the value Mod in order to set a default value, since maybeOpt returns Nothing if the option was not given on the command line (but it still shows the default value in the --help output.