Documentation

Tries to parse the supplied options against input arguments. If successful, parsed option callbacks are returned in Right. Otherwise an OptionsError is returned in Left.

Example program:

import System.Environment
import Text.LambdaOptions


options :: Options IO ()
options = do
    addOption (kw ["--help", "-h"] `text` "Display this help text.") $ \(HelpDescription desc) -> do
        putStrLn "Usage:"
        putStrLn desc
    addOption (kw "--user" `argText` "NAME" `text` "Prints name.") $ \name -> do
        putStrLn $ "Name:" ++ name
    addOption (kw "--user" `argText` "NAME AGE" `text` "Prints name and age.") $ \name age -> do
        putStrLn $ "Name:" ++ name ++ " Age:" ++ show (age :: Int)


main :: IO ()
main = do
    args <- getArgs
    case runOptions options args of
        Left (ParseFailed msg _ _) -> do
            putStrLn msg
            putStrLn $ getHelpDescription options
        Right action -> action

>>> example.exe --user John 20 --user Jane
Name:John Age:20
Name:Jane
>>> example.exe -h
Usage:
-h, --help                  Display this help text.
    --user NAME             Prints name.
    --user NAME AGE         Prints name and age.
>>> example.exe --user BadLuckBrian thirteen
Unknown option at index 2: `thirteen'
Usage:
-h, --help                  Display this help text.
    --user NAME             Prints name.
    --user NAME AGE         Prints name and age.

A monad for parsing options.

Contains information about what went wrong during an unsuccessful options parse.

Describes the callback f to be called for a successfully parsed option.

The function (or value) f can have any arity and ultimately returns a value with type Monad m => m ()

Each of the callback's arguments must have a type t which implements Parseable and Typeable.

Think of this as the following constraint synonym:

type OptionCallback m f = (Monad m, f ~ (Parseable t*, Typeable t*) => t0 -> t1 -> ... -> tN -> m ())

Example callbacks:

f0 = putStrLn "Option parsed!" :: IO ()
f1 = put :: String -> State String ()
f2 n = liftIO (print n) :: (MonadIO m) => Int -> m ()
f3 name year ratio = lift (print (name, year, ratio)) :: (MonadTrans m) => String -> Int -> Float -> m IO ()

Adds the supplied option to the Options m () context.

If the keyword is matched and the types of the callback's parameters can successfully be parsed, the callback is called with the parsed arguments.

When used as a callback argument, this contains the help description given by the added options.

Example:

addOption (kw ["--help", "-h"]) $ \(HelpDescription desc) -> do
    putStrLn desc

Produces the help description given by the input options.