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Contents |
- Argument Properties
- Evaluating the Command Line
- Extracting the Argument Values
- Placing additional Constraints on the Arguments
- Argument Error Reporting
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Description |
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. 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
dynamic 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
...
`catchDyn`
(\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. |
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Synopsis |
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Argument Properties |
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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. |
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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. | Instances | |
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type Argtester = String -> Maybe (ArgumentDescription -> String) |
Command line 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. |
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argdesc |
:: [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. |
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desc_short |
:: 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. |
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desc_long |
:: 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. |
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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. |
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desc_value_required :: ArgumentProperty |
Signal that the argument requires a value. |
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desc_value_optional :: ArgumentProperty |
Signal that the argument optionally has a value. The user may or may
not specify a value to this argument. |
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desc_times |
:: Int | Lower bound of the allowed number of times. | -> Int | Upper bound of the allowed number of times. | -> ArgumentProperty | The corresponding argument property. | Specify lower and upper bound on the number of times an argument may
occur. |
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desc_once |
:: 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. |
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desc_at_least_once |
:: ArgumentProperty | The corresponding argument property. | Signal that the argument must occur at least one time. |
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desc_at_most_once |
:: ArgumentProperty | The corresponding argument property. | Signal that the argument must occur at most one time. |
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desc_any_times |
:: ArgumentProperty | The corresponding argument property. | Signal that the argument may occur any number of times. |
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desc_at_least |
:: 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. |
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desc_at_most |
:: 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. |
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desc_argname |
:: 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. |
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desc_description |
:: 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. |
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desc_tester |
:: 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. |
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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.
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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.
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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) |
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Evaluating the Command Line |
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data Arguments |
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getargs |
:: 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 dynamic
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. |
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getargs_ordered |
:: 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 dynamic
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. |
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getargs' |
:: 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. |
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getargs_ordered' |
:: 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. |
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unsafe_getargs |
:: 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. In case of an error, it prints an error message, which contains the usage info, on stderr
and terminates the program with exitFailure. The parse result is returned (same as getarg's). GHC.IOBase.unsafePerformIO is used to take the
result out of the IO monad. The action is performed on demand, when the parse result is evaluated. It may result in the program being aborted. In order to avoid this happening
at unexpected times, the main function should, assuming that args is the result of unsafe_getargs, start with the line
seq args (return ()). This will trigger any command line argument errors at the beginning of the program, terminating it properly. 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 = do
seq args (return ())
... See getargs, unsafe_getargs_ordered.
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unsafe_getargs_ordered |
:: 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. See unsafe_getargs.
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Extracting the Argument Values |
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arg_switch |
:: 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. |
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arg_times |
:: 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. |
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args_opt |
:: 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. |
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args_req |
:: 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. |
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reqarg_opt |
:: 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. |
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reqarg_req |
:: 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. |
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optarg_opt |
:: 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). |
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optarg_req |
:: 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. |
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arg_occurs |
:: 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.
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Placing additional Constraints on the Arguments |
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args_none |
:: [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. |
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args_all |
:: [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. |
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args_one |
:: [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. |
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args_at_most_one |
:: [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. |
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args_at_least_one |
:: [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. |
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arg_conflicts |
:: 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. |
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Argument Error Reporting |
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data ArgError |
Error thrown as a dynamic exception when there is an error in the
command line arguments. | Constructors | ArgError | | argerror_message :: String | Error message generated by HsShellScript.Args. | argerror_usageinfo :: String | Usage information derived from the argument descriptions. |
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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. |
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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)". |
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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". |
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Produced by Haddock version 0.4 |