Documentation

A monad transformer for parsing options.

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

Convenience Keyword to build upon. Takes either a single alias or a list of name aliases to start with. Use record syntax to set the rest.

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

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

Example:

import System.Environment
import Text.LambdaOptions

options :: Options IO ()
options = do
    addOption (kw "--help") $ do
        putStrLn "--user NAME [AGE]"
    addOption (kw "--user") $ name -> do
        putStrLn $ Name: ++ name
    addOption (kw "--user") $ name age -> do
        putStrLn $ Name: ++ name ++ " Age:" ++ show (age :: Int)

main :: IO ()
main = do
    args <- getArgs
    mError <- runOptions options args
    case mError of
        Just (ParseFailed msg _ _) -> putStrLn msg
        Nothing -> return ()

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