The options package lets library and application developers easily work
with command-line options.
The following example is a full program that can accept two options,
--message and --quiet:
import Control.Applicative
import Options
data MainOptions = MainOptions
{ optMessage :: String
, optQuiet :: Bool
}
instance Options MainOptions where
defineOptions = pure MainOptions
<*> simpleOption "message" "Hello world!"
"A message to show the user."
<*> simpleOption "quiet" False
"Whether to be quiet."
main :: IO ()
main = runCommand $ \opts args -> do
if optQuiet opts
then return ()
else putStrLn (optMessage opts)
$ ./hello
Hello world!
$ ./hello --message='ciao mondo'
ciao mondo
$ ./hello --quiet
$
In addition, this library will automatically create documentation options
such as --help and --help-all:
$ ./hello --help
Help Options:
-h, --help
Show option summary.
--help-all
Show all help options.
Application Options:
--message :: text
A message to show the user.
default: "Hello world!"
--quiet :: bool
Whether to be quiet.
default: false
