Documentation

Create an option parser, equivalent to option. The second argument is the modifiers to add to the option, and can be defined by using function composition (.).

  someOption :: Opt Int
  someOption
    = option readParser
        ( long "someopt"
        . help "Some option"
        . defaultVal 256
        )

Create a flag parser, equivalent to option. The first argument is the default value (returned when the flag modifier is absent), and the second is the active value (returned when the flag modifier is present). The second argument is the modifiers to add to the option, and can be defined by using function composition (.).

  someFlag :: Opt Int
  someFlag
    = flag 0 1
        ( long "someflag"
        . help "Some flag"
        )

A flag parser, specialized to Bool. The parser (e.g. when parsing an environment variable) will accept true and false, but case insensitive, rather than using the Read instance for Bool. The default value is False, and the active value is True.

  someSwitch :: Opt Bool
  someSwitch
    = switch
        ( long "someswitch"
        . help "Some switch"
        )

Similar to switch, but the default value is True and the active is False.

Create an argument parser, equivalent to argument. The second argument is the modifiers to add to the option, and can be defined by using function composition (.).

  someArgument :: Opt Int
  someArgument
    = argument
        ( help "Some argument"
        . defaultVal "this is the default"
        )

Add a long modifier to an option

Add a short modifier to an option

Add help to an option

Add a metavar metavar to an option, to be displayed as the meta-parameter next to long/short modifiers

Specify an environment variable to lookup for an option

Add a default value to an option. Cannot be used in conjuction with with required, defaultStr or optional.

Add a default unparsed value to an option. Cannot be used in conjuction with defaultVal, required or optional.

Mark an option as required. Cannot be used in conjunction with optional, defaultVal or requiredStr.

Specify that an option is optional. This will convert an Opt a to an Opt (Maybe a). Cannot be used in conjunction with defaultVal, defaultStr or required.

Convert a parser that returns Maybe to a parser that returns Either, with the default Left value unable to parse: <input>.

A parser that uses the Read instance to parse into a type.

A parser that returns a string. Any type that has an instance of IsString will work, and this parser always succeeds.

A parser that returns a Bool. This will succeed for the strings true and false in a case-insensitive manner.

A parser that can parse many items, returning a list.

Class for options that can be optional. Cannot be used in conjunction with HasDefaultVal, HasDefaultStr or HasRequired. Note that this will turn a parser for a into a parser for Maybe a, modifying the reader function appropriately. For example:

  someOpt :: Opt (Maybe Int)
  someOpt
    = optionWith readParser
        ( long "someopt"
        . optional
        )

Class to convert an intermediate option type into Opt. Instances should set the appropriate _optType.