Distribution.GetOpt

The Haskell Cabal

Distribution.GetOpt

Portability	portable
Stability	experimental
Maintainer	libraries@haskell.org

Contents

GetOpt
Example

Description

Edited by Isaac Jones to allow non-options to pass through.

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.

Synopsis

getOpt :: ArgOrder a -> [OptDescr a] -> [String] -> ([a], [String], [String], [String])

usageInfo :: String -> [OptDescr a] -> String

data ArgOrder a

= RequireOrder

| Permute

| ReturnInOrder (String -> a)

data OptDescr a = Option [Char] [String] (ArgDescr a) String

data ArgDescr a

= NoArg a

| ReqArg (String -> a) String

| OptArg (Maybe String -> a) String

GetOpt

getOpt :: ArgOrder a -> [OptDescr a] -> [String] -> ([a], [String], [String], [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 getArgs).

getOpt returns a triple, consisting of the argument values, a list of non-option (commands, files, etc), a list of options that didn't match, and a list of error messages.

usageInfo :: String -> [OptDescr a] -> String

Return a string describing the usage of a command, derived from the header (first argument) and the options described by the second argument.

data ArgOrder a

What to do with options following non-options

Constructors

RequireOrder	no option processing after first non-option
Permute	freely intersperse options and non-options
ReturnInOrder (String -> a)	wrap non-options into options

data OptDescr a

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

Constructors

Option [Char] [String] (ArgDescr a) String

data ArgDescr a

Describes whether an option takes an argument or not, and if so how the argument is injected into a value of type a.

Constructors

NoArg a	no argument expected
ReqArg (String -> a) String	option requires argument
OptArg (Maybe String -> a) String	optional argument

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 GetOpt -- (not 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], [String])
    compilerOpts argv = 
    	case (getOpt Permute options argv) of
    	   (o,n,no,[]  ) -> return (o,n,no)
    	   (_,_,_,errs) -> ioError (userError (concat errs ++ usageInfo header options))
      where header = "Usage: ic [OPTION...] files..."

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