System.Console.ParseArgs

This module supplies an argument parser. Given a description of type [Arg] of the legal arguments to the program, a list of argument strings, and a bit of extra information, the parseArgs function in this module returns an Args data structure suitable for querying using the provided functions gotArg, getArg, etc.

Describing allowed arguments

The argument parser requires a description of the arguments that will be parsed. This is supplied as a list of Arg records, built up using the functions described here.

data Ord a => Arg a

The description of an argument, suitable for messages and for parsing. The argData field is used both for flags with a data argument, and for positional data arguments.

There are two cases:

1. The argument is a flag, in which case at least one of argAbbr and argName is provided;
2. The argument is positional, in which case neither argAbbr nor argName are provided, but argData is.

If none of argAbbr, argName, or argData are provided, this is an error. See also the argDataRequired, argDataOptional, and argDataDefaulted functions below, which are used to generate argData.

Constructors

Arg

Fields

argIndex :: a

Connects the input description to the output argument.

argAbbr :: Maybe Char

One-character flag name.

argName :: Maybe String

"Long name" of flag.

argData :: Maybe DataArg

Datum description.

argDesc :: String

Documentation for the argument.

data Argtype

The types of an argument carrying data. The constructor argument is used to carry a default value.

The constructor argument should really be hidden. Values of this type are normally constructed within the pseudo-constructors pseudo-constructors argDataRequired, argDataOptional, and argDataDefaulted, to which only the constructor function itself is passed.

Constructors

ArgtypeString (Maybe String)

ArgtypeInteger (Maybe Integer)

ArgtypeInt (Maybe Int)

ArgtypeDouble (Maybe Double)

ArgtypeFloat (Maybe Float)

data ArgsComplete

How "sloppy" the parse is.

Constructors

ArgsComplete

Any extraneous arguments (unparseable from description) will cause the parser to fail.

ArgsTrailing String

Trailing extraneous arguments are permitted, and will be skipped, saved, and returned. The constructor argument is the name of the args.

ArgsInterspersed

All extraneous arguments are permitted, and will be skipped, saved, and returned.

DataArg and its pseudo-constructors

data DataArg

Information specific to an argument carrying a datum. This is an opaque type, whose instances are constructed using the pseudo-constructors argDataRequired, argDataOptional, and argDataDefaulted.

argDataRequired

Arguments

:: String

Datum print name.

-> (Maybe a -> Argtype)

Type constructor for datum.

-> Maybe DataArg

Result is argData-ready.

Generate the argData for the given non-optional argument.

argDataOptional

Arguments

:: String

Datum print name.

-> (Maybe a -> Argtype)

Type constructor for datum.

-> Maybe DataArg

Result is argData-ready.

Generate the argData for the given optional argument with no default.

argDataDefaulted

Arguments

:: String

Datum print name.

-> (Maybe a -> Argtype)

Type constructor for datum.

-> a

Datum default value.

-> Maybe DataArg

Result is argData-ready.

Generate the argData for the given optional argument with the given default.

Argument processing

The argument descriptions are used to parse the command line arguments, and the results of the parse can later be (efficiently) queried to determine program behavior.

Getting parse results

The argument parser returns an opaque map from argument index to parsed argument data (plus some convenience information).

data ArgRecord a

The type of the mapping from argument index to value.

data Ord a => Args a

The data structure parseArgs produces. The key element is the ArgRecord args.

Constructors

Args

Fields

args :: ArgRecord a

The argument map.

argsProgName :: String

Basename of 0th argument.

argsUsage :: String

Full usage string.

argsRest :: [String]

Remaining unprocessed arguments.

parseArgs

Arguments

:: (Show a, Ord a)

=> ArgsComplete

Degree of completeness of parse.

-> [Arg a]

Argument descriptions.

-> String

Full program pathname.

-> [String]

Incoming program argument list.

-> Args a

Outgoing argument parse results.

Given a description of the arguments, parseArgs produces a map from the arguments to their "values" and some other useful byproducts. parseArgs requires that the argument descriptions occur in the order 1) flag arguments, 2) required positional arguments, 3) optional positional arguments; otherwise a runtime error will be thrown.

parseArgsIO

Arguments

:: (Show a, Ord a)

=> ArgsComplete

Degree of completeness of parse.

-> [Arg a]

Argument descriptions.

-> IO (Args a)

Argument parse results.

Most of the time, you just want the environment's arguments and are willing to live in the IO monad. This version of parseArgs digs the pathname and arguments out of the system directly.

Using parse results

Query functions permit checking for the existence and values of command-line arguments.

gotArg

Arguments

:: Ord a

=> Args a

Parsed arguments.

-> a

Index of argument to be checked for.

-> Bool

True if the arg was present.

Check whether a given optional argument was supplied. Works on all types.

class ArgType b where

Type of values that can be parsed by the argument parser.

Methods

getArg

Arguments

:: (Show a, Ord a)

=> Args a

Parsed arguments.

-> a

Index of argument to be retrieved.

-> Maybe b

Argument value if present. |Fetch the value of a required argument.

Fetch an argument's value if it is present.

getRequiredArg

Arguments

:: (Show a, Ord a)

=> Args a

Parsed arguments.

-> a

Index of argument to be retrieved.

-> b

Argument value.

Instances

ArgType Double

ArgType Float

ArgType Int

ArgType Integer

ArgType ()

ArgType ArgFileOpener

ArgType [Char]

getArgString

Arguments

:: (Show a, Ord a)

=> Args a

Parsed arguments.

-> a

Index of argument to be retrieved.

-> Maybe String

Argument value if present.

Deprecated

Return the String value, if any, of the given argument.

getArgFile

Arguments

:: (Show a, Ord a)

=> Args a

Parsed arguments.

-> a

Index of argument to be retrieved.

-> IOMode

IO mode the file should be opened in.

-> IO (Maybe Handle)

Handle of opened file, if the argument was present.

Deprecated

Treat the String value, if any, of the given argument as a file handle and try to open it as requested.

getArgStdio

Arguments

:: (Show a, Ord a)

=> Args a

Parsed arguments.

-> a

Index of argument to be retrieved.

-> IOMode

IO mode the file should be opened in. Must not be ReadWriteMode.

-> IO Handle

Appropriate file handle.

Treat the String value, if any, of the given argument as a file handle and try to open it as requested. If not present, substitute the appropriate one of stdin or stdout as indicated by IOMode.

getArgInteger

Arguments

:: (Show a, Ord a)

=> Args a

Parsed arguments.

-> a

Index of argument to be retrieved.

-> Maybe Integer

Argument value if present.

Deprecated

Return the Integer value, if any, of the given argument.

getArgInt

Arguments

:: (Show a, Ord a)

=> Args a

Parsed arguments.

-> a

Index of argument to be retrieved.

-> Maybe Int

Argument value if present.

Deprecated

Return the Int value, if any, of the given argument.

getArgDouble

Arguments

:: (Show a, Ord a)

=> Args a

Parsed arguments.

-> a

Index of argument to be retrieved.

-> Maybe Double

Argument value if present.

Deprecated

Return the Double value, if any, of the given argument.

getArgFloat

Arguments

:: (Show a, Ord a)

=> Args a

Parsed arguments.

-> a

Index of argument to be retrieved.

-> Maybe Float

Argument value if present.

Deprecated

Return the Float value, if any, of the given argument.

newtype ArgFileOpener

ArgType instance for opening a file from its string name.

Constructors

ArgFileOpener

Fields

argFileOpener :: IOMode -> IO Handle

Function to open the file

Instances

ArgType ArgFileOpener

Misc

data ParseArgsException

This exception is raised with an appropriate error message when argument parsing fails. The first argument is the usage message, the second the actual error message from the parser.

Constructors

ParseArgsException String String

Instances

Eq ParseArgsException

Show ParseArgsException

Typeable ParseArgsException

Exception ParseArgsException

baseName

Arguments

:: String

Pathname.

-> String

Rightmost component of pathname.

Return the filename part of a pathname. Unnecessarily efficient implementation does a single tail-call traversal with no construction.

parseError

Arguments

:: String

Usage message.

-> String

Specific error message.

-> a

Bogus polymorphic result.

Generate a usage error with the given supplementary message string.

usageError :: Ord a => Args a -> String -> b

Generate a usage error with the given supplementary message string.

data IOMode

See openFile

Constructors

ReadMode

WriteMode

AppendMode

Instances

Enum IOMode

Eq IOMode

Ord IOMode

Read IOMode

Show IOMode

Ix IOMode