Documentation

Tries to parse the supplied options against input arguments. If successful, parsed option callbacks are executed. Otherwise none of the callbacks are executed.

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
    result <- runOptions options args
    case result of
        Left (ParseFailed msg _ _) -> do
            putStrLn msg
            desc <- getHelpDescription options
            putStrLn desc
        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 transformer for parsing options.

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

An option keyword, such as "--help"

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.

Convenience Keyword creation class.

Shorthand for toKeyword.

Sets the kwText field in the keyword. Intended to be used infix.

kw "--quiet" `text` "Suppress message display."

Sets the kwArgText field in the keyword. Intended to be used infix:

kw "--directory" `argText` "DIR" `text` "Write files to DIR."

Class describing parseable values. Much like the Read class.

A simple wrapper over [a]. Used to avoid overlapping instances for Parseable [a] and Parseable String