System/Console/GetOpt.hs

{-# 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 : experimental
-- 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 Prelude -- necessary to get dependencies right

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

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 decription of options
usageInfo header optDescr = unlines (header:table)
 where (ss,ls,ds) = (unzip3 . concatMap fmtOpt) optDescr
 table = zipWith3 paste (sameLen ss) (sameLen ls) ds
 paste x y z = " " ++ x ++ " " ++ y ++ " " ++ z
 sameLen xs = flushLeft ((maximum . map length) xs) xs
 flushLeft n xs = [ take n (x ++ repeat ' ') | x <- xs ]

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

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

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

{-|
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 ordering optDescr args = (os,xs,es ++ map errUnrec us)
 where (os,xs,us,es) = getOpt' ordering optDescr 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' _ _ [] = ([],[],[],[])
getOpt' ordering optDescr (arg:args) = procNextOpt opt ordering
 where procNextOpt (Opt o) _ = (o:os,xs,us,es)
 procNextOpt (UnreqOpt u) _ = (os,xs,u:us,es)
 procNextOpt (NonOpt x) RequireOrder = ([],x:rest,[],[])
 procNextOpt (NonOpt x) Permute = (os,x:xs,us,es)
 procNextOpt (NonOpt x) (ReturnInOrder f) = (f x :os, xs,us,es)
 procNextOpt EndOfOpts RequireOrder = ([],rest,[],[])
 procNextOpt EndOfOpts Permute = ([],rest,[],[])
 procNextOpt EndOfOpts (ReturnInOrder f) = (map f rest,[],[],[])
 procNextOpt (OptErr e) _ = (os,xs,us,e:es)

 (opt,rest) = getNext arg args optDescr
 (os,xs,us,es) = getOpt' ordering optDescr 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 ('-':'-':[]) rest _ = (EndOfOpts,rest)
getNext ('-':'-':xs) rest optDescr = longOpt xs rest optDescr
getNext ('-': x :xs) rest optDescr = shortOpt x xs rest optDescr
getNext a rest _ = (NonOpt a,rest)

-- handle long option
longOpt :: String -> [String] -> [OptDescr a] -> (OptKind a,[String])
longOpt ls rs optDescr = long ads arg rs
 where (opt,arg) = break (=='=') ls
 getWith p = [ o | o@(Option _ xs _ _) <- optDescr
 , find (p opt) xs /= Nothing ]
 exact = getWith (==)
 options = if null exact then getWith isPrefixOf else exact
 ads = [ ad | Option _ _ ad _ <- options ]
 optStr = ("--"++opt)

 long (_:_:_) _ rest = (errAmbig options optStr,rest)
 long [NoArg a ] [] rest = (Opt a,rest)
 long [NoArg _ ] ('=':_) rest = (errNoArg optStr,rest)
 long [ReqArg _ d] [] [] = (errReq d optStr,[])
 long [ReqArg f _] [] (r:rest) = (Opt (f r),rest)
 long [ReqArg f _] ('=':xs) rest = (Opt (f xs),rest)
 long [OptArg f _] [] rest = (Opt (f Nothing),rest)
 long [OptArg f _] ('=':xs) rest = (Opt (f (Just xs)),rest)
 long _ _ rest = (UnreqOpt ("--"++ls),rest)

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

 short (_:_:_) _ rest = (errAmbig options optStr,rest)
 short (NoArg a :_) [] rest = (Opt a,rest)
 short (NoArg a :_) xs rest = (Opt a,('-':xs):rest)
 short (ReqArg _ d:_) [] [] = (errReq d optStr,[])
 short (ReqArg f _:_) [] (r:rest) = (Opt (f r),rest)
 short (ReqArg f _:_) xs rest = (Opt (f xs),rest)
 short (OptArg f _:_) [] rest = (Opt (f Nothing),rest)
 short (OptArg f _:_) xs rest = (Opt (f (Just xs)),rest)
 short [] [] rest = (UnreqOpt optStr,rest)
 short [] xs rest = (UnreqOpt optStr,('-':xs):rest)

-- miscellaneous error formatting

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

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

errUnrec :: String -> String
errUnrec optStr = "unrecognized option `" ++ optStr ++ "'\n"

errNoArg :: String -> OptKind a
errNoArg optStr = OptErr ("option `" ++ optStr ++ "' 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.

-}