-- #hide
{- This ist GetOpt from GHC 6.2.2. GHC 6.4's GetOpt is buggy - the "--" argument
   is no longer recognized. Therefore I include the old GetOpt here.
   HsShellScript.Args uses it.
-}

module HsShellScript.GetOpt (
        -- * GetOpt
 getOpt,
 usageInfo,
 ArgOrder(..),
 OptDescr(..),
 ArgDescr(..),

 -- * Example
  
 -- $example
  ) where

import Prelude
import Data.List  ( isPrefixOf )

-- |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

data OptKind a                -- kind of cmd line arg (internal use only):
   = Opt       a                --    an 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 decription 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 a b. (a -> b) -> [a] -> [b]
map 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) = (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),
                                    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),
                                    String
descr)
   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

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 argument values, a list
of options that didn\'t match, and a list of error messages.
-}
getOpt :: ArgOrder a                   -- non-option handling
       -> [OptDescr a]                 -- option descriptors
       -> [String]                     -- the commandline arguments
       -> ([a],[String],[String])      -- (options,non-options,error messages)
getOpt :: forall a.
ArgOrder a -> [OptDescr a] -> [String] -> ([a], [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])
procNextOpt OptKind a
opt ArgOrder a
ordering
   where procNextOpt :: OptKind a -> ArgOrder a -> ([a], [String], [String])
procNextOpt (Opt a
o)    ArgOrder a
_                 = (a
oa -> [a] -> [a]
forall a. a -> [a] -> [a]
:[a]
os,[String]
xs,[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]
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]
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
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]
es) = ArgOrder a -> [OptDescr a] -> [String] -> ([a], [String], [String])
forall a.
ArgOrder a -> [OptDescr a] -> [String] -> ([a], [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]
ls ArgDescr a
_ String
_) <- [OptDescr a]
optDescr, String
l <- [String]
ls, String
opt String -> String -> Bool
`p` String
l ]
         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
errUnrec String
optStr,[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
x String
xs [String]
rest [OptDescr a]
optDescr = [ArgDescr a] -> String -> [String] -> (OptKind a, [String])
short [ArgDescr a]
ads String
xs [String]
rest
  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
x 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
x]

        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
errUnrec String
optStr,[String]
rest)
        short []             String
xs [String]
rest     = (String -> OptKind a
forall a. String -> OptKind a
errUnrec 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 -> OptKind a
errUnrec :: forall a. String -> OptKind a
errUnrec String
optStr = String -> OptKind a
forall a. String -> OptKind a
OptErr (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
-----------------------------------------------------------------------------------------
-}

{- $example

To hopefully illuminate the role of the different data
structures, here\'s the command-line options for a (very simple)
compiler:

>    module Opts 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 "stdout"
>    
>    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..."

-}