HsShellScript.Args

This module provides a more convient way of parsing command line arguments than the GHC GetOpt package. It makes use of GetOpt, but hides it from the user. It is reexported from module HsShellScript.

For each command line argument, a description is to be created with argdesc. Then the command line arguments are evaluated with one of the getargs... functions. In case of an error, this will cause a exception, which provides an expressive error message to be printed. Then the arg... functions are used to extract the values contained in the arguments, with the right type. The typical use of HsShellScript.Args looks something like this:

import HsShellScript

main =
   do let a_onevalue = argdesc [ desc_at_most_once, ... ]
          a_values   = argdesc [ desc_direct, ... ]
          a_switch   = argdesc [ ... ]
          ...
          header = "mclapep - My Command Line Argument Parser Example Program, version 1.0.0"

      args <- getargs header [a_onevalue, a_values, a_switch, ...]

      val  <- optarg_req a_onevalue args        -- val  :: Maybe String
      vals <- args_req   a_values args          -- vals :: [String]
      doit <- arg_switch a_switch args          -- doit :: Bool
      ...
   `catch` 
      (\argerror -> do
          hPutStrLn stderr $ (argerror_message argerror) ++ "\n\n" ++ (argerror_usageinfo argerror)
          exitFailure
      )

Errors in the argument descriptions are regarded as bugs, and handled by aborting the program with a message which is meaningful to the programmer. It is assumed that the argument description is a constant for a given program.

Errors in the arguments are reported using HsShellScript's error handling scheme. An error description value is generated, and either returned via an Either value, or thrown as an exception.

Argument Properties

data ArgumentProperty

A property of a command line argument. These are generated by the desc_... functions, and condensed to argument descriptions of type ArgumentDescription by argdesc. This type is abstract.

data ArgumentDescription

Description of one command line argument. These are generated by argdesc from a list of argument properties, and subsequently used by one of the getargs... functions. This type is abstract.

Constructors

ArgumentDescription

Fields

argdesc_short_args :: [Char]

Short option names

argdesc_long_args :: [String]

Long option names

argdesc_argarg :: ArgumentValueSpec

What about a possible value of the argument?

argdesc_times :: Maybe (Int, Int)

Minimum and maximum of number of occurences allowed

argdesc_argargname :: Maybe String

Name for argument's value, for message generation

argdesc_argarg_description :: Maybe String

Descrition of the argument, for message generation

argdesc_argarg_tester :: Maybe Argtester

Argument value tester

Instances

Eq ArgumentDescription

Ord ArgumentDescription

data ArgumentValueSpec

Does the command line argument take an value?

Constructors

ArgumentValue_none

No value

ArgumentValue_required

Value required

ArgumentValue_optional

Value optional

Instances

Eq ArgumentValueSpec

Ord ArgumentValueSpec

Show ArgumentValueSpec

type Argtester = String -> Maybe (ArgumentDescription -> String)

Argument value tester function. This tests the format of an argument's value for errors. The tester function is specified by desc_tester or such, as part of the argument description.

The tester is passed the argument value. If the format is correct, then it returns Nothing. If there is an error, then it returns Just msgf, with msgf being an error message generation function. This function gets passed the argument description, and produces the error message. The argument description typically is used to extract a descriptive name of the argument (using argname or argname_a) to be included in the error message.

argdesc

Arguments

:: [ArgumentProperty]

List of properties, which describe the command line argument.

-> ArgumentDescription

The corresponding argument description.

Make an argument description from a list of argument properties. This condenses the list to an argument description, which can be uses by the getargs... functions and the argument value extraction functions.

desc_short

Arguments

:: Char

The character to name the argument.

-> ArgumentProperty

The corresponding argument property.

Short name of the argument. This specifies a character for a one letter style argument, like -x. There can be specified several for the same argument. Each argument needs at least either a short or a long name.

desc_long

Arguments

:: String

The long name of the argument.

-> ArgumentProperty

The corresponding argument property.

Long name of the argument. This specifies a GNU style long name for the argument, like --arg or --arg=.... There can be specified several names for the same argument. Each argument needs at least either a short or a long name.

desc_direct :: ArgumentProperty

Signal that this is the description of direct arguments. Direct arguments are the ones not introduced by any short or long argument names (like -x or --arg), or which occur after the special argument --. The presence of desc_direct in the argument properties list signals argdesc that this is the description of the direct arguments. There may be at most one such description.

desc_value_required :: ArgumentProperty

Signal that the argument requires a value.

desc_value_optional :: ArgumentProperty

Signal that the argument optionally has a value. The user may or may not specify a value to this argument.

desc_times

Arguments

:: Int

Lower bound of the allowed number of argdesc_times.

-> Int

Upper bound of the allowed number of argdesc_times.

-> ArgumentProperty

The corresponding argument property.

Specify lower and upper bound on the number of times an argument may occur.

desc_once

Arguments

:: ArgumentProperty

The corresponding argument property.

Signal that the argument must be present exactly once. This is meaningful only for arguments which can take a value.

desc_at_least_once

Arguments

:: ArgumentProperty

The corresponding argument property.

Signal that the argument must occur at least one time.

desc_at_most_once

Arguments

:: ArgumentProperty

The corresponding argument property.

Signal that the argument must occur at most one time.

desc_any_times

Arguments

:: ArgumentProperty

The corresponding argument property.

Signal that the argument may occur any number of times.

desc_at_least

Arguments

:: Int

Number of times.

-> ArgumentProperty

The corresponding argument property.

Signal that the argument must have at least the specified number of occurences, and has no upper limit of occurences.

desc_at_most

Arguments

:: Int

Number of times.

-> ArgumentProperty

The corresponding argument property.

Signal that the argument does not need to be present, and may occur at most the specified number of times.

desc_argname

Arguments

:: String

Name of the argument's value.

-> ArgumentProperty

The corresponding argument property.

Specify the descriptive name for command line argument's value. Used for the generation of the usage message. The name should be very short.

desc_description

Arguments

:: String

Short description of the argument.

-> ArgumentProperty

The corresponding argument property.

Specify a short description of what the argument does. Used for the generation of the usage message. This is to fit on one line, after the short and long argument names. It should be 40 characters long or so.

desc_tester

Arguments

:: Argtester

Argument tester to apply to this argument

-> ArgumentProperty

The corresponding argument property.

Specify a tester for this argument. The tester is a function which tests the argument value for format errors. Typically, it tests whether the value can be parsed to some target type. If the test fails, the tester produces an error message. When parsing the command line arguments (which getargs or related), all the testers are applied to the respective argument values, and an ArgError is thrown in case of failure. By using a tester, it can be ensured that the argument values abide a specific format when extracting them, such that they can be parsed without errors, e.g. myarg = read (reqarg_req args d_myarg).

An argument tester is a function of type Argtester.

See readtester, desc_integer, desc_nonneg_integer, Argtester.

desc_integer :: ArgumentProperty

Specify that the value of this argument, if present, is a positive integer. This will cause an error when the command line is parsed, and the argument's value doesn't specify an integer.

desc_integer = desc_tester (readtester (reads :: ReadS Int) "Integer expected.")

See desc_tester.

desc_nonneg_integer :: ArgumentProperty

Specify that the value of this argument, if present, is a non-negative integer. This will cause an error when the command line is parsed, and the value doesn't specify a non-negative integer.

desc_nonneg_integer = desc_tester (readtester ((filter (\(a,_) -> a >= 0) . reads) :: ReadS Int) "Non-negative integer expected." )

See desc_tester.

readtester :: ReadS a -> String -> Argtester

Build an argument tester from a reads like function. Typically, a specialisation of the standard prelude function read is used. Example: readtester "Integer expected." (reads :: ReadS Int)

Evaluating the Command Line

data Arguments

This represents the parsed contents of the command line. It is returned by the getargs... functions, and passed on to the value extraction functions by the user.

See getargs, getargs_ordered, 'getargs\'', 'getargs_ordered\''.

getargs

Arguments

:: String

Header to be used in the usage info.

-> [ArgumentDescription]

The argument descriptions.

-> IO Arguments

The contents of the command line.

Parse command line arguments. The arguments are taken from a call to getArgs and parsed. Any error is thrown as a ArgError exception. The result is a value from which the information in the command line can be extracted by the arg..., reqarg... and optarg... functions.

Named arguments (like -x or --arg) and direct arguments may occur in any order.

getargs_ordered

Arguments

:: String

Header to be used in the usage info.

-> [ArgumentDescription]

Descriptions of the arguments.

-> IO Arguments

The contents of the command line.

Parse command line arguments. The arguments are taken from a call to getArgs and parsed. Any error is thrown as a ArgError exception. The result is a value from which the information in the command line can be extracted by the arg..., reqarg... and optarg... functions.

All arguments after the first direct argument are regarded as direct arguments. This means that argument names introduced by - or -- no longer take effect.

getargs'

Arguments

:: String

Header to be used in the usage info.

-> [String]

Command line to be parsed.

-> [ArgumentDescription]

The argument descriptions.

-> Either ArgError Arguments

The contents of the command line.

Parse the specified command line. Any error is returned as Left argerror. In case of success, the result is returned as Right res. From the result, the information in the command line can be extracted by the arg..., reqarg... and optarg... functions.

Named arguments (like -x or --arg) and direct arguments may occur in any order.

getargs_ordered'

Arguments

:: String

Header to be used in the usage info.

-> [String]

Command line to be parsed.

-> [ArgumentDescription]

The argument descriptions.

-> Either ArgError Arguments

The contents of the command line.

Parse the specified command line. Any error is returned as Left argerror. In case of success, the result is returned as Right res. From the result, the information in the command line can be extracted by the arg..., reqarg... and optarg... functions.

All arguments after the first direct argument are regarded as direct arguments. This means that argument names introduced by - or -- no longer take effect.

unsafe_getargs

Arguments

:: String

The header used in the usage information

-> [ArgumentDescription]

The argument descriptions

-> Arguments

The parsed command line arguments

getargs as a pure function, instead of an IO action. This allows to make evaluated command line arguments global values. This calls getargs to parse the command line arguments. GHC.IO.unsafePerformIO is used to take the result out of the IO monad.

unsafe_getargs header descs = GHC.IO.unsafePerformIO $ getargs header descs

The getargs action is performed on demand, when the parse result is evaluated. It may result in an ArgError being thrown. In order to avoid this happening at unexpected times, the main function should, start with the line seq args (return ()), where args is the result of unsafe_getargs,. This will trigger any command line argument errors at the beginning of the program. (See section 6.2 of the Hakell Report for the definition of seq).

A typical use of unsafe_getargs looks like this:

header = "..."
descs = [ d_myflag, ... ]

d_myflag = argdesc [ ... ]

args = unsafe_getargs header descs
myflag = arg_switch args d_myflag

main = mainwrapper $ do
   seq args (return ())
   ...

See getargs, unsafe_getargs_ordered.

unsafe_getargs_ordered

Arguments

:: String

The header used in the usage information

-> [ArgumentDescription]

The argument descriptions

-> Arguments

The parsed command line arguments

getargs_ordered as a pure function, instead of an IO action. This is exactly like unsafe_getargs, but using getargs_ordered instead of getargs.

unsafe_getargs_ordered = GHC.IO.unsafePerformIO $ getargs_ordered header descs

See unsafe_getargs.

Extracting the Argument Values

arg_switch

Arguments

:: Arguments

Command line parse result.

-> ArgumentDescription

Argument description of the switch.

-> Bool

Whether the switch is present in the command line.

Query whether a certain switch is specified on the command line. A switch is an argument which is allowed zero or one time, and has no value.

arg_times

Arguments

:: Arguments

Command line parse result.

-> ArgumentDescription

Description of the argument.

-> Int

Number of times the argument occurs.

Query the number of occurences of an argument.

args_opt

Arguments

:: Arguments

Command line parse result.

-> ArgumentDescription

Description of the argument.

-> [Maybe String]

The occurences of the argument.

Query the values of an argument with optional value. This is for arguments which take an optional value, and may occur several times. The occurences with value are represented as Just value, the occurences without are represented as Nothing.

args_req

Arguments

:: Arguments

Command line parse result.

-> ArgumentDescription

Description of the argument.

-> [String]

The values of the argument.

Query the values of an argument with required value. This is for arguments which require a value, and may occur several times.

reqarg_opt

Arguments

:: Arguments

Command line parse result.

-> ArgumentDescription

Description of the argument.

-> Maybe String

The value of the argument, if it occurs.

Query the optional value of a required argument. This is for arguments which must occur once, and may have a value. If the argument is specified, its value is returned as Just value. If it isn't, the result is Nothing.

reqarg_req

Arguments

:: Arguments

Command line parse result.

-> ArgumentDescription

Description of the argument.

-> String

The value of the argument.

Query the value of a required argument. This is for arguments which must occur exactly once, and require a value.

optarg_opt

Arguments

:: Arguments

Command line parse result.

-> ArgumentDescription

Description of the argument.

-> Maybe (Maybe String)

The occurence of the argument and its value (see above).

Query the optional value of an optional argument. This is for arguments which may occur zero or one time, and which may or may not have a value. If the argument doesn't occur, the result is Nothing. If it does occur, but has no value, then the result is Just Nothing. If it does occur with value, the result is Just (Just value).

optarg_req

Arguments

:: Arguments

Command line parse result.

-> ArgumentDescription

Description of the argument.

-> Maybe String

The value of the argument, if it occurs.

Query the value of an optional argument. This is for optional arguments which require a value, and may occur at most once. The result is Just value if the argument occurs, and Nothing if it doesn't occur.

arg_occurs

Arguments

:: Arguments

Command line parse result.

-> ArgumentDescription

Description of the respective argument.

-> Bool

Whether the specified argument occurs in the command line.

Whether the specified argument occurs in the command line.

Placing additional Constraints on the Arguments

args_none

Arguments

:: [ArgumentDescription]

List of the arguments which must not be present.

-> Arguments

Command line parse result.

-> IO ()

None of the specifed arguments may be present.

Throws an ArgError if any of the arguments are present.

args_all

Arguments

:: [ArgumentDescription]

List of the arguments which must be present.

-> Arguments

Command line parse result.

-> IO ()

All of the specified arguments must be present.

Throws an ArgError if any is missing.

args_one

Arguments

:: [ArgumentDescription]

List of the arguments, of which exactly one must be present.

-> Arguments

Command line parse result.

-> IO ()

Exactly one of the specified arguments must be present.

Otherwise throw an ArgError.

args_at_most_one

Arguments

:: [ArgumentDescription]

List of the arguments, of which at most one may be present.

-> Arguments

Command line parse result.

-> IO ()

At most one of the specified arguments may be present.

Otherwise throw an ArgError.

args_at_least_one

Arguments

:: [ArgumentDescription]

List of the arguments, of which at least one must be present.

-> Arguments

Command line parse result.

-> IO ()

At least one of the specified arguments must be present.

Otherwise throw an ArgError.

arg_conflicts

Arguments

:: ArgumentDescription

Argument which doesn't tolerate the other arguments

-> [ArgumentDescription]

Arguments which aren't tolerated by the specified argument

-> Arguments

Command line parse result.

-> IO ()

When the specified argument is present, then none of the other arguments may be present.

Otherwise throw an ArgError.

Argument Error Reporting

data ArgError

Error thrown when there is an error in the command line arguments.

Constructors

ArgError

Fields

argerror_message :: String

Error message generated by HsShellScript.Args.

argerror_usageinfo :: String

Usage information derived from the argument descriptions.

Instances

Show ArgError

Typeable ArgError

Exception ArgError

Make ArgError an instance of Exception, so we can throw and catch it, using GHC-6.10's new exception library.

usage_info :: Arguments -> String

Get the usage information from the parsed arguments. The usage info contains the header specified to the corresponding getargs... function, and descriptions of the command line arguments.

argname :: ArgumentDescription -> String

Generate a descriptive argument name from an argument description, suitable for use in error messages. This uses the long and short argument names (as specified by desc_short and desc_long) and generates descriptive names of the argument like "-f", "-myflag", "-f/--myflag", etc. All the argument names are included. In case of direct arguments (see desc_direct), the descriptive name is "(direct argument)".

argname_a :: ArgumentDescription -> String

Generate a descriptive argument name from an argument description, beginning with "argument". This uses the long and short argument names (as specified by desc_short and desc_long) and generates descriptive names of the argument like "argument -f", "argument -myflag", "argument -f/--myflag", etc. All the argument names are included. In case of direct arguments (see desc_direct), the descriptive name is "direct argument".