Options are defined together in a single data type, which will be an instance of Options

See defineOptions for details on defining instances of Options.

An options value containing only the default values for each option

This is equivalent to the options value when parsing an empty argument list.

Defines a new option in the current options type

Either calls the given continuation, prints help text and calls exitSuccess, or prints an error and calls exitFailure.

See runSubcommand for details on subcommand support.

Used to run applications that are split into subcommands

See parseOptions and parseSubcommand

Get the error that prevented options from being parsed from argv, or Nothing if no error was detected

Get a help message to show the user

If the arguments included a help flag, this will be a message appropriate to that flag. Otherwise, it is a summary (equivalent to --help).

This is always a non-empty string, regardless of whether the parse succeeded or failed. If you need to perform additional validation on the options value, this message can be displayed if validation fails.

See parseOptions

Get the options value that was parsed from argv, or Nothing if the arguments could not be converted into options

Note: This function return Nothing if the user provided a help flag. To check whether an error occurred during parsing, check the value of parsedError.

Get command-line arguments remaining after parsing options

The arguments are unchanged from the original argument list, and have not been decoded or otherwise transformed.

Attempt to convert a list of command-line arguments into an options value

See parseSubcommand

Get the subcommand action that was parsed from argv, or Nothing if the arguments could not be converted into a valid action

Note: This function return Nothing if the user provided a help flag. To check whether an error occurred during parsing, check the value of parsedError.

Attempt to convert a list of command-line arguments into a subcommand action

An option's type determines how the option will be parsed, and which Haskell type the parsed value will be stored as

There are many types available, covering most basic types and a few more advanced types.

Defines a new option in the current options type

All options must have one or more flags. Options may also have a default value, a description, and a group.

The flags are how the user specifies an option on the command line. Flags may be short or long. See optionShortFlags and optionLongFlags for details.

defineOption optionType_word16 (\o -> o
   { optionLongFlags = ["port"]
   , optionDefault = 80
   })

Short flags are a single character. When entered by a user, they are preceded by a dash and possibly other short flags.

Short flags must be a letter or a number.

Example: An option with optionShortFlags = ['p'] may be set using:

$ ./app -p 443
$ ./app -p443

Long flags are multiple characters. When entered by a user, they are preceded by two dashes.

Long flags may contain letters, numbers, '-', and '_'.

Example: An option with optionLongFlags = ["port"] may be set using:

$ ./app --port 443
$ ./app --port=443

Options may have a default value. This will be parsed as if the user had entered it on the command line.

An option's description is used with the default implementation of --help. It should be a short string describing what the option does.

Which group the option is in. See the "Option groups" section for details.

Define an option group with the given name and title

Use groupDescription to add additional descriptive text, if needed.

A short title for the group, which is used when printing --help output.

A description of the group, which is used when printing --help output.

Store an option as a Bool

The option's value must be either "true" or "false". Boolean options are unary, which means that their value is optional when specified on the command line.

Store an option value as a String

The value is decoded to Unicode first, if needed.

Store an option as an Int

The option value must be an integer n such that minBound <= n <= maxBound.

Store an option as an Int8

The option value must be an integer n such that minBound <= n <= maxBound.

Store an option as an Int16

The option value must be an integer n such that minBound <= n <= maxBound.

Store an option as an Int32

The option value must be an integer n such that minBound <= n <= maxBound.

Store an option as an Int64

The option value must be an integer n such that minBound <= n <= maxBound.

Store an option as a Word

The option value must be a positive integer n such that 0 <= n <= maxBound.

Store an option as a Word8

The option value must be a positive integer n such that 0 <= n <= maxBound.

Store an option as a Word16

The option value must be a positive integer n such that 0 <= n <= maxBound.

Store an option as a Word32

The option value must be a positive integer n such that 0 <= n <= maxBound.

Store an option as a Word64

The option value must be a positive integer n such that 0 <= n <= maxBound.

Store an option as an Integer

The option value must be an integer. There is no minimum or maximum value.

Store an option as a Float

The option value must be a number. Due to the imprecision of floating-point math, the stored value might not exactly match the user's input. If the user's input is out of range for the Float type, it will be stored as Infinity or -Infinity.

Store an option as a Double

The option value must be a number. Due to the imprecision of floating-point math, the stored value might not exactly match the user's input. If the user's input is out of range for the Double type, it will be stored as Infinity or -Infinity.

Store an option as a Maybe of another type

The value will be Nothing if the option is set to an empty string.

Store an option as a list, using another option type for the elements

The separator should be a character that will not occur within the values, such as a comma or semicolon.

Store an option as a Set, using another option type for the elements

The separator should be a character that will not occur within the values, such as a comma or semicolon.

Duplicate elements in the input are permitted.

Store an option as a Map, using other option types for the keys and values

The item separator is used to separate key/value pairs from each other. It should be a character that will not occur within either the keys or values.

The value separator is used to separate the key from the value. It should be a character that will not occur within the keys. It may occur within the values.

Duplicate keys in the input are permitted. The final value for each key is stored.

Store an option as one of a set of possible values

This is a simplistic implementation, useful for quick scripts. For more possibilities, see optionType.

Define a new option type with the given name, default, and behavior

The name of this option type; used in --help output.

The default value for options of this type. This will be used if optionDefault is not set when defining the option.

Try to parse the given string to an option value. If parsing fails, an error message will be returned.

Format the value for display; used in --help output.

If not Nothing, then options of this type may be set by a unary flag. The option will be parsed as if the given value were set.

If not Nothing, then options of this type may be set with repeated flags. Each flag will be parsed with optionTypeParse, and the resulting parsed values will be passed to this function for merger into the final value.