haskell-options: An easy-to-use command-line option parser for Haskell

The options package lets library and application developers easily work with command-line options.

Code: https://john-millikin.com/code/haskell-options (GitHub mirror)


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.
    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
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