    {-# LANGUAGE Safe #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  System.Console.GetOpt
    -- Copyright   :  (c) Sven Panne 2002-2005
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  stable
    -- Portability :  portable
    --
    -- This library provides facilities for parsing the command-line options
    -- in a standalone program.  It is essentially a Haskell port of the GNU
    -- @getopt@ library.
    --
    -----------------------------------------------------------------------------

    {-
    Sven Panne <Sven.Panne@informatik.uni-muenchen.de> Oct. 1996 (small
    changes Dec. 1997)

    Two rather obscure features are missing: The Bash 2.0 non-option hack
    (if you don't already know it, you probably don't want to hear about
    it...) and the recognition of long options with a single dash
    (e.g. '-help' is recognised as '--help', as long as there is no short
    option 'h').

    Other differences between GNU's getopt and this implementation:

    * To enforce a coherent description of options and arguments, there
      are explanation fields in the option/argument descriptor.

    * Error messages are now more informative, but no longer POSIX
      compliant... :-(

    And a final Haskell advertisement: The GNU C implementation uses well
    over 1100 lines, we need only 195 here, including a 46 line example!
    :-)
    -}

    module System.Console.GetOpt (
       -- * GetOpt
       getOpt, getOpt',
       usageInfo,
       ArgOrder(..),
       OptDescr(..),
       ArgDescr(..),

       -- * Examples

       -- |To hopefully illuminate the role of the different data structures,
       -- here are the command-line options for a (very simple) compiler,
       -- done in two different ways.
       -- The difference arises because the type of 'getOpt' is
       -- parameterized by the type of values derived from flags.

       -- ** Interpreting flags as concrete values
       -- $example1

       -- ** Interpreting flags as transformations of an options record
       -- $example2
    ) where

    import Data.List ( isPrefixOf, find )

    -- |What to do with options following non-options
    data ArgOrder a
      = RequireOrder                -- ^ no option processing after first non-option
      | Permute                     -- ^ freely intersperse options and non-options
      | ReturnInOrder (String -> a) -- ^ wrap non-options into options

    {-|
    Each 'OptDescr' describes a single option.

    The arguments to 'Option' are:

    * list of short option characters

    * list of long option strings (without \"--\")

    * argument descriptor

    * explanation of option for user
    -}
    data OptDescr a =              -- description of a single options:
       Option [Char]                --    list of short option characters
              [String]              --    list of long option strings (without "--")
              (ArgDescr a)          --    argument descriptor
              String                --    explanation of option for user

    -- |Describes whether an option takes an argument or not, and if so
    -- how the argument is injected into a value of type @a@.
    data ArgDescr a
       = NoArg                   a         -- ^   no argument expected
       | ReqArg (String       -> a) String -- ^   option requires argument
       | OptArg (Maybe String -> a) String -- ^   optional argument

    -- | @since 4.7.0.0
    instance Functor ArgOrder where
        fmap :: forall a b. (a -> b) -> ArgOrder a -> ArgOrder b
    fmap a -> b
    _ ArgOrder a
    RequireOrder      = ArgOrder b
    forall a. ArgOrder a
    RequireOrder
        fmap a -> b
    _ ArgOrder a
    Permute           = ArgOrder b
    forall a. ArgOrder a
    Permute
        fmap a -> b
    f (ReturnInOrder String -> a
    g) = (String -> b) -> ArgOrder b
    forall a. (String -> a) -> ArgOrder a
    ReturnInOrder (a -> b
    f (a -> b) -> (String -> a) -> String -> b
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> a
    g)

    -- | @since 4.7.0.0
    instance Functor OptDescr where
        fmap :: forall a b. (a -> b) -> OptDescr a -> OptDescr b
    fmap a -> b
    f (Option String
    a [String]
    b ArgDescr a
    argDescr String
    c) = String -> [String] -> ArgDescr b -> String -> OptDescr b
    forall a. String -> [String] -> ArgDescr a -> String -> OptDescr a
    Option String
    a [String]
    b ((a -> b) -> ArgDescr a -> ArgDescr b
    forall a b. (a -> b) -> ArgDescr a -> ArgDescr b
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap a -> b
    f ArgDescr a
    argDescr) String
    c

    -- | @since 4.7.0.0
    instance Functor ArgDescr where
        fmap :: forall a b. (a -> b) -> ArgDescr a -> ArgDescr b
    fmap a -> b
    f (NoArg a
    a)    = b -> ArgDescr b
    forall a. a -> ArgDescr a
    NoArg (a -> b
    f a
    a)
        fmap a -> b
    f (ReqArg String -> a
    g String
    s) = (String -> b) -> String -> ArgDescr b
    forall a. (String -> a) -> String -> ArgDescr a
    ReqArg (a -> b
    f (a -> b) -> (String -> a) -> String -> b
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> a
    g) String
    s
        fmap a -> b
    f (OptArg Maybe String -> a
    g String
    s) = (Maybe String -> b) -> String -> ArgDescr b
    forall a. (Maybe String -> a) -> String -> ArgDescr a
    OptArg (a -> b
    f (a -> b) -> (Maybe String -> a) -> Maybe String -> b
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Maybe String -> a
    g) String
    s

    data OptKind a                -- kind of cmd line arg (internal use only):
       = Opt       a                --    an option
       | UnreqOpt  String           --    an un-recognized option
       | NonOpt    String           --    a non-option
       | EndOfOpts                  --    end-of-options marker (i.e. "--")
       | OptErr    String           --    something went wrong...

    -- | Return a string describing the usage of a command, derived from
    -- the header (first argument) and the options described by the
    -- second argument.
    usageInfo :: String                    -- header
              -> [OptDescr a]              -- option descriptors
              -> String                    -- nicely formatted description of options
    usageInfo :: forall a. String -> [OptDescr a] -> String
    usageInfo String
    header [OptDescr a]
    optDescr = [String] -> String
    unlines (String
    headerString -> [String] -> [String]
    forall a. a -> [a] -> [a]
    :[String]
    table)
       where ([String]
    ss,[String]
    ls,[String]
    ds)     = ([(String, String, String)] -> ([String], [String], [String])
    forall a b c. [(a, b, c)] -> ([a], [b], [c])
    unzip3 ([(String, String, String)] -> ([String], [String], [String]))
    -> ([OptDescr a] -> [(String, String, String)])
    -> [OptDescr a]
    -> ([String], [String], [String])
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (OptDescr a -> [(String, String, String)])
    -> [OptDescr a] -> [(String, String, String)]
    forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
    concatMap OptDescr a -> [(String, String, String)]
    forall a. OptDescr a -> [(String, String, String)]
    fmtOpt) [OptDescr a]
    optDescr
             table :: [String]
    table          = (String -> String -> String -> String)
    -> [String] -> [String] -> [String] -> [String]
    forall a b c d. (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d]
    zipWith3 String -> String -> String -> String
    paste ([String] -> [String]
    sameLen [String]
    ss) ([String] -> [String]
    sameLen [String]
    ls) [String]
    ds
             paste :: String -> String -> String -> String
    paste String
    x String
    y String
    z    = String
    "  " String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    x String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "  " String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    y String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "  " String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    z
             sameLen :: [String] -> [String]
    sameLen [String]
    xs     = Int -> [String] -> [String]
    flushLeft (([Int] -> Int
    forall a. Ord a => [a] -> a
    forall (t :: * -> *) a. (Foldable t, Ord a) => t a -> a
    maximum ([Int] -> Int) -> ([String] -> [Int]) -> [String] -> Int
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (String -> Int) -> [String] -> [Int]
    forall a b. (a -> b) -> [a] -> [b]
    map String -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length) [String]
    xs) [String]
    xs
             flushLeft :: Int -> [String] -> [String]
    flushLeft Int
    n [String]
    xs = [ Int -> String -> String
    forall a. Int -> [a] -> [a]
    take Int
    n (String
    x String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ Char -> String
    forall a. a -> [a]
    repeat Char
    ' ') | String
    x <- [String]
    xs ]

    fmtOpt :: OptDescr a -> [(String,String,String)]
    fmtOpt :: forall a. OptDescr a -> [(String, String, String)]
    fmtOpt (Option String
    sos [String]
    los ArgDescr a
    ad String
    descr) =
       case String -> [String]
    lines String
    descr of
         []     -> [(String
    sosFmt,String
    losFmt,String
    "")]
         (String
    d:[String]
    ds) ->  (String
    sosFmt,String
    losFmt,String
    d) (String, String, String)
    -> [(String, String, String)] -> [(String, String, String)]
    forall a. a -> [a] -> [a]
    : [ (String
    "",String
    "",String
    d') | String
    d' <- [String]
    ds ]
       where sepBy :: Char -> [String] -> String
    sepBy Char
    _  []     = String
    ""
             sepBy Char
    _  [String
    x]    = String
    x
             sepBy Char
    ch (String
    x:[String]
    xs) = String
    x String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ Char
    chChar -> String -> String
    forall a. a -> [a] -> [a]
    :Char
    ' 'Char -> String -> String
    forall a. a -> [a] -> [a]
    :Char -> [String] -> String
    sepBy Char
    ch [String]
    xs
             sosFmt :: String
    sosFmt = Char -> [String] -> String
    sepBy Char
    ',' ((Char -> String) -> String -> [String]
    forall a b. (a -> b) -> [a] -> [b]
    map (ArgDescr a -> Char -> String
    forall a. ArgDescr a -> Char -> String
    fmtShort ArgDescr a
    ad) String
    sos)
             losFmt :: String
    losFmt = Char -> [String] -> String
    sepBy Char
    ',' ((String -> String) -> [String] -> [String]
    forall a b. (a -> b) -> [a] -> [b]
    map (ArgDescr a -> String -> String
    forall a. ArgDescr a -> String -> String
    fmtLong  ArgDescr a
    ad) [String]
    los)

    fmtShort :: ArgDescr a -> Char -> String
    fmtShort :: forall a. ArgDescr a -> Char -> String
    fmtShort (NoArg  a
    _   ) Char
    so = String
    "-" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ [Char
    so]
    fmtShort (ReqArg String -> a
    _ String
    ad) Char
    so = String
    "-" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ [Char
    so] String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    " " String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    ad
    fmtShort (OptArg Maybe String -> a
    _ String
    ad) Char
    so = String
    "-" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ [Char
    so] String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "[" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    ad String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "]"

    fmtLong :: ArgDescr a -> String -> String
    fmtLong :: forall a. ArgDescr a -> String -> String
    fmtLong (NoArg  a
    _   ) String
    lo = String
    "--" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    lo
    fmtLong (ReqArg String -> a
    _ String
    ad) String
    lo = String
    "--" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    lo String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "=" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    ad
    fmtLong (OptArg Maybe String -> a
    _ String
    ad) String
    lo = String
    "--" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    lo String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "[=" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    ad String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "]"

    {-|
    Process the command-line, and return the list of values that matched
    (and those that didn\'t). The arguments are:

    * The order requirements (see 'ArgOrder')

    * The option descriptions (see 'OptDescr')

    * The actual command line arguments (presumably got from
      'System.Environment.getArgs').

    'getOpt' returns a triple consisting of the option arguments, a list
    of non-options, and a list of error messages.
    -}
    getOpt :: ArgOrder a                   -- non-option handling
           -> [OptDescr a]                 -- option descriptors
           -> [String]                     -- the command-line arguments
           -> ([a],[String],[String])      -- (options,non-options,error messages)
    getOpt :: forall a.
    ArgOrder a -> [OptDescr a] -> [String] -> ([a], [String], [String])
    getOpt ArgOrder a
    ordering [OptDescr a]
    optDescr [String]
    args = ([a]
    os,[String]
    xs,[String]
    es [String] -> [String] -> [String]
    forall a. [a] -> [a] -> [a]
    ++ (String -> String) -> [String] -> [String]
    forall a b. (a -> b) -> [a] -> [b]
    map String -> String
    errUnrec [String]
    us)
       where ([a]
    os,[String]
    xs,[String]
    us,[String]
    es) = ArgOrder a
    -> [OptDescr a] -> [String] -> ([a], [String], [String], [String])
    forall a.
    ArgOrder a
    -> [OptDescr a] -> [String] -> ([a], [String], [String], [String])
    getOpt' ArgOrder a
    ordering [OptDescr a]
    optDescr [String]
    args

    {-|
    This is almost the same as 'getOpt', but returns a quadruple
    consisting of the option arguments, a list of non-options, a list of
    unrecognized options, and a list of error messages.
    -}
    getOpt' :: ArgOrder a                         -- non-option handling
            -> [OptDescr a]                       -- option descriptors
            -> [String]                           -- the command-line arguments
            -> ([a],[String], [String] ,[String]) -- (options,non-options,unrecognized,error messages)
    getOpt' :: forall a.
    ArgOrder a
    -> [OptDescr a] -> [String] -> ([a], [String], [String], [String])
    getOpt' ArgOrder a
    _        [OptDescr a]
    _        []         =  ([],[],[],[])
    getOpt' ArgOrder a
    ordering [OptDescr a]
    optDescr (String
    arg:[String]
    args) = OptKind a -> ArgOrder a -> ([a], [String], [String], [String])
    procNextOpt OptKind a
    opt ArgOrder a
    ordering
       where procNextOpt :: OptKind a -> ArgOrder a -> ([a], [String], [String], [String])
    procNextOpt (Opt a
    o)      ArgOrder a
    _                 = (a
    oa -> [a] -> [a]
    forall a. a -> [a] -> [a]
    :[a]
    os,[String]
    xs,[String]
    us,[String]
    es)
             procNextOpt (UnreqOpt String
    u) ArgOrder a
    _                 = ([a]
    os,[String]
    xs,String
    uString -> [String] -> [String]
    forall a. a -> [a] -> [a]
    :[String]
    us,[String]
    es)
             procNextOpt (NonOpt String
    x)   ArgOrder a
    RequireOrder      = ([],String
    xString -> [String] -> [String]
    forall a. a -> [a] -> [a]
    :[String]
    rest,[],[])
             procNextOpt (NonOpt String
    x)   ArgOrder a
    Permute           = ([a]
    os,String
    xString -> [String] -> [String]
    forall a. a -> [a] -> [a]
    :[String]
    xs,[String]
    us,[String]
    es)
             procNextOpt (NonOpt String
    x)   (ReturnInOrder String -> a
    f) = (String -> a
    f String
    x a -> [a] -> [a]
    forall a. a -> [a] -> [a]
    :[a]
    os, [String]
    xs,[String]
    us,[String]
    es)
             procNextOpt OptKind a
    EndOfOpts    ArgOrder a
    RequireOrder      = ([],[String]
    rest,[],[])
             procNextOpt OptKind a
    EndOfOpts    ArgOrder a
    Permute           = ([],[String]
    rest,[],[])
             procNextOpt OptKind a
    EndOfOpts    (ReturnInOrder String -> a
    f) = ((String -> a) -> [String] -> [a]
    forall a b. (a -> b) -> [a] -> [b]
    map String -> a
    f [String]
    rest,[],[],[])
             procNextOpt (OptErr String
    e)   ArgOrder a
    _                 = ([a]
    os,[String]
    xs,[String]
    us,String
    eString -> [String] -> [String]
    forall a. a -> [a] -> [a]
    :[String]
    es)

             (OptKind a
    opt,[String]
    rest) = String -> [String] -> [OptDescr a] -> (OptKind a, [String])
    forall a.
    String -> [String] -> [OptDescr a] -> (OptKind a, [String])
    getNext String
    arg [String]
    args [OptDescr a]
    optDescr
             ([a]
    os,[String]
    xs,[String]
    us,[String]
    es) = ArgOrder a
    -> [OptDescr a] -> [String] -> ([a], [String], [String], [String])
    forall a.
    ArgOrder a
    -> [OptDescr a] -> [String] -> ([a], [String], [String], [String])
    getOpt' ArgOrder a
    ordering [OptDescr a]
    optDescr [String]
    rest

    -- take a look at the next cmd line arg and decide what to do with it
    getNext :: String -> [String] -> [OptDescr a] -> (OptKind a,[String])
    getNext :: forall a.
    String -> [String] -> [OptDescr a] -> (OptKind a, [String])
    getNext (Char
    '-':Char
    '-':[]) [String]
    rest [OptDescr a]
    _        = (OptKind a
    forall a. OptKind a
    EndOfOpts,[String]
    rest)
    getNext (Char
    '-':Char
    '-':String
    xs) [String]
    rest [OptDescr a]
    optDescr = String -> [String] -> [OptDescr a] -> (OptKind a, [String])
    forall a.
    String -> [String] -> [OptDescr a] -> (OptKind a, [String])
    longOpt String
    xs [String]
    rest [OptDescr a]
    optDescr
    getNext (Char
    '-': Char
    x :String
    xs) [String]
    rest [OptDescr a]
    optDescr = Char -> String -> [String] -> [OptDescr a] -> (OptKind a, [String])
    forall a.
    Char -> String -> [String] -> [OptDescr a] -> (OptKind a, [String])
    shortOpt Char
    x String
    xs [String]
    rest [OptDescr a]
    optDescr
    getNext String
    a            [String]
    rest [OptDescr a]
    _        = (String -> OptKind a
    forall a. String -> OptKind a
    NonOpt String
    a,[String]
    rest)

    -- handle long option
    longOpt :: String -> [String] -> [OptDescr a] -> (OptKind a,[String])
    longOpt :: forall a.
    String -> [String] -> [OptDescr a] -> (OptKind a, [String])
    longOpt String
    ls [String]
    rs [OptDescr a]
    optDescr = [ArgDescr a] -> String -> [String] -> (OptKind a, [String])
    long [ArgDescr a]
    ads String
    arg [String]
    rs
       where (String
    opt,String
    arg) = (Char -> Bool) -> String -> (String, String)
    forall a. (a -> Bool) -> [a] -> ([a], [a])
    break (Char -> Char -> Bool
    forall a. Eq a => a -> a -> Bool
    ==Char
    '=') String
    ls
             getWith :: (String -> String -> Bool) -> [OptDescr a]
    getWith String -> String -> Bool
    p = [ OptDescr a
    o | o :: OptDescr a
    o@(Option String
    _ [String]
    xs ArgDescr a
    _ String
    _) <- [OptDescr a]
    optDescr
                             , (String -> Bool) -> [String] -> Maybe String
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Maybe a
    find (String -> String -> Bool
    p String
    opt) [String]
    xs Maybe String -> Maybe String -> Bool
    forall a. Eq a => a -> a -> Bool
    /= Maybe String
    forall a. Maybe a
    Nothing ]
             exact :: [OptDescr a]
    exact     = (String -> String -> Bool) -> [OptDescr a]
    getWith String -> String -> Bool
    forall a. Eq a => a -> a -> Bool
    (==)
             options :: [OptDescr a]
    options   = if [OptDescr a] -> Bool
    forall a. [a] -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null [OptDescr a]
    exact then (String -> String -> Bool) -> [OptDescr a]
    getWith String -> String -> Bool
    forall a. Eq a => [a] -> [a] -> Bool
    isPrefixOf else [OptDescr a]
    exact
             ads :: [ArgDescr a]
    ads       = [ ArgDescr a
    ad | Option String
    _ [String]
    _ ArgDescr a
    ad String
    _ <- [OptDescr a]
    options ]
             optStr :: String
    optStr    = (String
    "--"String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++String
    opt)

             long :: [ArgDescr a] -> String -> [String] -> (OptKind a, [String])
    long (ArgDescr a
    _:ArgDescr a
    _:[ArgDescr a]
    _)      String
    _        [String]
    rest     = ([OptDescr a] -> String -> OptKind a
    forall a. [OptDescr a] -> String -> OptKind a
    errAmbig [OptDescr a]
    options String
    optStr,[String]
    rest)
             long [NoArg  a
    a  ] []       [String]
    rest     = (a -> OptKind a
    forall a. a -> OptKind a
    Opt a
    a,[String]
    rest)
             long [NoArg  a
    _  ] (Char
    '=':String
    _)  [String]
    rest     = (String -> OptKind a
    forall a. String -> OptKind a
    errNoArg String
    optStr,[String]
    rest)
             long [ReqArg String -> a
    _ String
    d] []       []       = (String -> String -> OptKind a
    forall a. String -> String -> OptKind a
    errReq String
    d String
    optStr,[])
             long [ReqArg String -> a
    f String
    _] []       (String
    r:[String]
    rest) = (a -> OptKind a
    forall a. a -> OptKind a
    Opt (String -> a
    f String
    r),[String]
    rest)
             long [ReqArg String -> a
    f String
    _] (Char
    '=':String
    xs) [String]
    rest     = (a -> OptKind a
    forall a. a -> OptKind a
    Opt (String -> a
    f String
    xs),[String]
    rest)
             long [OptArg Maybe String -> a
    f String
    _] []       [String]
    rest     = (a -> OptKind a
    forall a. a -> OptKind a
    Opt (Maybe String -> a
    f Maybe String
    forall a. Maybe a
    Nothing),[String]
    rest)
             long [OptArg Maybe String -> a
    f String
    _] (Char
    '=':String
    xs) [String]
    rest     = (a -> OptKind a
    forall a. a -> OptKind a
    Opt (Maybe String -> a
    f (String -> Maybe String
    forall a. a -> Maybe a
    Just String
    xs)),[String]
    rest)
             long [ArgDescr a]
    _            String
    _        [String]
    rest     = (String -> OptKind a
    forall a. String -> OptKind a
    UnreqOpt (String
    "--"String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++String
    ls),[String]
    rest)

    -- handle short option
    shortOpt :: Char -> String -> [String] -> [OptDescr a] -> (OptKind a,[String])
    shortOpt :: forall a.
    Char -> String -> [String] -> [OptDescr a] -> (OptKind a, [String])
    shortOpt Char
    y String
    ys [String]
    rs [OptDescr a]
    optDescr = [ArgDescr a] -> String -> [String] -> (OptKind a, [String])
    short [ArgDescr a]
    ads String
    ys [String]
    rs
      where options :: [OptDescr a]
    options = [ OptDescr a
    o  | o :: OptDescr a
    o@(Option String
    ss [String]
    _ ArgDescr a
    _ String
    _) <- [OptDescr a]
    optDescr, Char
    s <- String
    ss, Char
    y Char -> Char -> Bool
    forall a. Eq a => a -> a -> Bool
    == Char
    s ]
            ads :: [ArgDescr a]
    ads     = [ ArgDescr a
    ad | Option String
    _ [String]
    _ ArgDescr a
    ad String
    _ <- [OptDescr a]
    options ]
            optStr :: String
    optStr  = Char
    '-'Char -> String -> String
    forall a. a -> [a] -> [a]
    :[Char
    y]

            short :: [ArgDescr a] -> String -> [String] -> (OptKind a, [String])
    short (ArgDescr a
    _:ArgDescr a
    _:[ArgDescr a]
    _)        String
    _  [String]
    rest     = ([OptDescr a] -> String -> OptKind a
    forall a. [OptDescr a] -> String -> OptKind a
    errAmbig [OptDescr a]
    options String
    optStr,[String]
    rest)
            short (NoArg  a
    a  :[ArgDescr a]
    _) [] [String]
    rest     = (a -> OptKind a
    forall a. a -> OptKind a
    Opt a
    a,[String]
    rest)
            short (NoArg  a
    a  :[ArgDescr a]
    _) String
    xs [String]
    rest     = (a -> OptKind a
    forall a. a -> OptKind a
    Opt a
    a,(Char
    '-'Char -> String -> String
    forall a. a -> [a] -> [a]
    :String
    xs)String -> [String] -> [String]
    forall a. a -> [a] -> [a]
    :[String]
    rest)
            short (ReqArg String -> a
    _ String
    d:[ArgDescr a]
    _) [] []       = (String -> String -> OptKind a
    forall a. String -> String -> OptKind a
    errReq String
    d String
    optStr,[])
            short (ReqArg String -> a
    f String
    _:[ArgDescr a]
    _) [] (String
    r:[String]
    rest) = (a -> OptKind a
    forall a. a -> OptKind a
    Opt (String -> a
    f String
    r),[String]
    rest)
            short (ReqArg String -> a
    f String
    _:[ArgDescr a]
    _) String
    xs [String]
    rest     = (a -> OptKind a
    forall a. a -> OptKind a
    Opt (String -> a
    f String
    xs),[String]
    rest)
            short (OptArg Maybe String -> a
    f String
    _:[ArgDescr a]
    _) [] [String]
    rest     = (a -> OptKind a
    forall a. a -> OptKind a
    Opt (Maybe String -> a
    f Maybe String
    forall a. Maybe a
    Nothing),[String]
    rest)
            short (OptArg Maybe String -> a
    f String
    _:[ArgDescr a]
    _) String
    xs [String]
    rest     = (a -> OptKind a
    forall a. a -> OptKind a
    Opt (Maybe String -> a
    f (String -> Maybe String
    forall a. a -> Maybe a
    Just String
    xs)),[String]
    rest)
            short []             [] [String]
    rest     = (String -> OptKind a
    forall a. String -> OptKind a
    UnreqOpt String
    optStr,[String]
    rest)
            short []             String
    xs [String]
    rest     = (String -> OptKind a
    forall a. String -> OptKind a
    UnreqOpt String
    optStr,(Char
    '-'Char -> String -> String
    forall a. a -> [a] -> [a]
    :String
    xs)String -> [String] -> [String]
    forall a. a -> [a] -> [a]
    :[String]
    rest)

    -- miscellaneous error formatting

    errAmbig :: [OptDescr a] -> String -> OptKind a
    errAmbig :: forall a. [OptDescr a] -> String -> OptKind a
    errAmbig [OptDescr a]
    ods String
    optStr = String -> OptKind a
    forall a. String -> OptKind a
    OptErr (String -> [OptDescr a] -> String
    forall a. String -> [OptDescr a] -> String
    usageInfo String
    header [OptDescr a]
    ods)
       where header :: String
    header = String
    "option `" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    optStr String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "' is ambiguous; could be one of:"

    errReq :: String -> String -> OptKind a
    errReq :: forall a. String -> String -> OptKind a
    errReq String
    d String
    optStr = String -> OptKind a
    forall a. String -> OptKind a
    OptErr (String
    "option `" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    optStr String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "' requires an argument " String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    d String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "\n")

    errUnrec :: String -> String
    errUnrec :: String -> String
    errUnrec String
    optStr = String
    "unrecognized option `" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    optStr String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "'\n"

    errNoArg :: String -> OptKind a
    errNoArg :: forall a. String -> OptKind a
    errNoArg String
    optStr = String -> OptKind a
    forall a. String -> OptKind a
    OptErr (String
    "option `" String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    optStr String -> String -> String
    forall a. [a] -> [a] -> [a]
    ++ String
    "' doesn't allow an argument\n")

    {-
    -----------------------------------------------------------------------------------------
    -- and here a small and hopefully enlightening example:

    data Flag = Verbose | Version | Name String | Output String | Arg String   deriving Show

    options :: [OptDescr Flag]
    options =
       [Option ['v']     ["verbose"]           (NoArg Verbose)      "verbosely list files",
        Option ['V','?'] ["version","release"] (NoArg Version)      "show version info",
        Option ['o']     ["output"]            (OptArg out "FILE")  "use FILE for dump",
        Option ['n']     ["name"]              (ReqArg Name "USER") "only dump USER's files"]

    out :: Maybe String -> Flag
    out Nothing  = Output "stdout"
    out (Just o) = Output o

    test :: ArgOrder Flag -> [String] -> String
    test order cmdline = case getOpt order options cmdline of
                            (o,n,[]  ) -> "options=" ++ show o ++ "  args=" ++ show n ++ "\n"
                            (_,_,errs) -> concat errs ++ usageInfo header options
       where header = "Usage: foobar [OPTION...] files..."

    -- example runs:
    -- putStr (test RequireOrder ["foo","-v"])
    --    ==> options=[]  args=["foo", "-v"]
    -- putStr (test Permute ["foo","-v"])
    --    ==> options=[Verbose]  args=["foo"]
    -- putStr (test (ReturnInOrder Arg) ["foo","-v"])
    --    ==> options=[Arg "foo", Verbose]  args=[]
    -- putStr (test Permute ["foo","--","-v"])
    --    ==> options=[]  args=["foo", "-v"]
    -- putStr (test Permute ["-?o","--name","bar","--na=baz"])
    --    ==> options=[Version, Output "stdout", Name "bar", Name "baz"]  args=[]
    -- putStr (test Permute ["--ver","foo"])
    --    ==> option `--ver' is ambiguous; could be one of:
    --          -v      --verbose             verbosely list files
    --          -V, -?  --version, --release  show version info
    --        Usage: foobar [OPTION...] files...
    --          -v        --verbose             verbosely list files
    --          -V, -?    --version, --release  show version info
    --          -o[FILE]  --output[=FILE]       use FILE for dump
    --          -n USER   --name=USER           only dump USER's files
    -----------------------------------------------------------------------------------------
    -}

    {- $example1

    A simple choice for the type associated with flags is to define a type
    @Flag@ as an algebraic type representing the possible flags and their
    arguments:

    >    module Opts1 where
    >
    >    import System.Console.GetOpt
    >    import Data.Maybe ( fromMaybe )
    >
    >    data Flag
    >     = Verbose  | Version
    >     | Input String | Output String | LibDir String
    >       deriving Show
    >
    >    options :: [OptDescr Flag]
    >    options =
    >     [ Option ['v']     ["verbose"] (NoArg Verbose)       "chatty output on stderr"
    >     , Option ['V','?'] ["version"] (NoArg Version)       "show version number"
    >     , Option ['o']     ["output"]  (OptArg outp "FILE")  "output FILE"
    >     , Option ['c']     []          (OptArg inp  "FILE")  "input FILE"
    >     , Option ['L']     ["libdir"]  (ReqArg LibDir "DIR") "library directory"
    >     ]
    >
    >    inp,outp :: Maybe String -> Flag
    >    outp = Output . fromMaybe "stdout"
    >    inp  = Input  . fromMaybe "stdin"
    >
    >    compilerOpts :: [String] -> IO ([Flag], [String])
    >    compilerOpts argv =
    >       case getOpt Permute options argv of
    >          (o,n,[]  ) -> return (o,n)
    >          (_,_,errs) -> ioError (userError (concat errs ++ usageInfo header options))
    >      where header = "Usage: ic [OPTION...] files..."

    Then the rest of the program will use the constructed list of flags
    to determine it\'s behaviour.

    -}

    {- $example2

    A different approach is to group the option values in a record of type
    @Options@, and have each flag yield a function of type
    @Options -> Options@ transforming this record.

    >    module Opts2 where
    >
    >    import System.Console.GetOpt
    >    import Data.Maybe ( fromMaybe )
    >
    >    data Options = Options
    >     { optVerbose     :: Bool
    >     , optShowVersion :: Bool
    >     , optOutput      :: Maybe FilePath
    >     , optInput       :: Maybe FilePath
    >     , optLibDirs     :: [FilePath]
    >     } deriving Show
    >
    >    defaultOptions    = Options
    >     { optVerbose     = False
    >     , optShowVersion = False
    >     , optOutput      = Nothing
    >     , optInput       = Nothing
    >     , optLibDirs     = []
    >     }
    >
    >    options :: [OptDescr (Options -> Options)]
    >    options =
    >     [ Option ['v']     ["verbose"]
    >         (NoArg (\ opts -> opts { optVerbose = True }))
    >         "chatty output on stderr"
    >     , Option ['V','?'] ["version"]
    >         (NoArg (\ opts -> opts { optShowVersion = True }))
    >         "show version number"
    >     , Option ['o']     ["output"]
    >         (OptArg ((\ f opts -> opts { optOutput = Just f }) . fromMaybe "output")
    >                 "FILE")
    >         "output FILE"
    >     , Option ['c']     []
    >         (OptArg ((\ f opts -> opts { optInput = Just f }) . fromMaybe "input")
    >                 "FILE")
    >         "input FILE"
    >     , Option ['L']     ["libdir"]
    >         (ReqArg (\ d opts -> opts { optLibDirs = optLibDirs opts ++ [d] }) "DIR")
    >         "library directory"
    >     ]
    >
    >    compilerOpts :: [String] -> IO (Options, [String])
    >    compilerOpts argv =
    >       case getOpt Permute options argv of
    >          (o,n,[]  ) -> return (foldl (flip id) defaultOptions o, n)
    >          (_,_,errs) -> ioError (userError (concat errs ++ usageInfo header options))
    >      where header = "Usage: ic [OPTION...] files..."

    Similarly, each flag could yield a monadic function transforming a record,
    of type @Options -> IO Options@ (or any other monad), allowing option
    processing to perform actions of the chosen monad, e.g. printing help or
    version messages, checking that file arguments exist, etc.

    -}