Documentation

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.

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"
        )

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.

Wrap a symbol in quotes, for pretty printing in type errors.

Check if x is not an element of the type-level list xs. If it is print the appropriate error message using l and r for clarity.