Options.Applicative.Builder

Parser builders

This module contains utility functions and combinators to create parsers for individual options.

Each parser builder takes an option modifier. A modifier can be created by composing the basic modifiers provided by this module using the Monoid operations mempty and mappend, or their aliases idm and <>.

For example:

out = strOption
    ( long "output"
   <> short 'o'
   <> metavar "FILENAME" )

creates a parser for an option called "output".

subparser :: Mod CommandFields a -> Parser a

Builder for a command parser. The command modifier can be used to specify individual commands.

strArgument :: Mod ArgumentFields String -> Parser String

Builder for a String argument.

argument :: ReadM a -> Mod ArgumentFields a -> Parser a

Builder for an argument parser.

flag

Arguments

:: a

default value

-> a

active value

-> Mod FlagFields a

option modifier

-> Parser a

Builder for a flag parser.

A flag that switches from a "default value" to an "active value" when encountered. For a simple boolean value, use switch instead.

flag'

Arguments

:: a

active value

-> Mod FlagFields a

option modifier

-> Parser a

Builder for a flag parser without a default value.

Same as flag, but with no default value. In particular, this flag will never parse successfully by itself.

It still makes sense to use it as part of a composite parser. For example

length <$> many (flag' () (short 't'))

is a parser that counts the number of "-t" arguments on the command line.

switch :: Mod FlagFields Bool -> Parser Bool

Builder for a boolean flag.

switch = flag False True

abortOption :: ParseError -> Mod OptionFields (a -> a) -> Parser (a -> a)

An option that always fails.

When this option is encountered, the option parser immediately aborts with the given parse error. If you simply want to output a message, use infoOption instead.

infoOption :: String -> Mod OptionFields (a -> a) -> Parser (a -> a)

An option that always fails and displays a message.

strOption :: Mod OptionFields String -> Parser String

Builder for an option taking a String argument.

option :: ReadM a -> Mod OptionFields a -> Parser a

Builder for an option using the given reader.

nullOption :: ReadM a -> Mod OptionFields a -> Parser a

Deprecated: Use option instead

Same as option.

Modifiers

short :: HasName f => Char -> Mod f a

Specify a short name for an option.

long :: HasName f => String -> Mod f a

Specify a long name for an option.

help :: String -> Mod f a

Specify the help text for an option.

helpDoc :: Maybe Doc -> Mod f a

Specify the help text for an option as a Doc value.

value :: HasValue f => a -> Mod f a

Specify a default value for an option.

Note: Because this modifier means the parser will never fail, do not use it with combinators such as some or many, as these combinators continue until a failure occurs. Careless use will thus result in a hang.

showDefaultWith :: (a -> String) -> Mod f a

Specify a function to show the default value for an option.

showDefault :: Show a => Mod f a

Show the default value for this option using its Show instance.

metavar :: HasMetavar f => String -> Mod f a

Specify a metavariable for the argument.

Metavariables have no effect on the actual parser, and only serve to specify the symbolic name for an argument to be displayed in the help text.

eitherReader :: (String -> Either String a) -> ReadM a

Convert a function in the Either monad to a reader.

noArgError :: ParseError -> Mod OptionFields a

Specify the error to display when no argument is provided to this option.

data ParseError

Constructors

ErrorMsg String

InfoMsg String

ShowHelpText

UnknownError

MissingError (OptTree (Chunk Doc))

Instances

Show ParseError

Monoid ParseError

hidden :: Mod f a

Hide this option from the brief description.

internal :: Mod f a

Hide this option from the help text

command :: String -> ParserInfo a -> Mod CommandFields a

Add a command to a subparser option.

completeWith :: HasCompleter f => [String] -> Mod f a

Add a list of possible completion values.

action :: HasCompleter f => String -> Mod f a

Add a bash completion action. Common actions include file and directory. See http://www.gnu.org/software/bash/manual/html_node/Programmable-Completion-Builtins.html#Programmable-Completion-Builtins for a complete list.

completer :: HasCompleter f => Completer -> Mod f a

Add a completer to an argument.

A completer is a function String -> IO String which, given a partial argument, returns all possible completions for that argument.

idm :: Monoid m => m

Trivial option modifier.

(<>) :: Monoid m => m -> m -> m infixr 6

An infix synonym for mappend.

Since: 4.5.0.0

mappend :: Monoid a => a -> a -> a

An associative operation

Readers

A collection of basic Option readers.

auto :: Read a => ReadM a

Option reader based on the Read type class.

str :: ReadM String

String Option reader.

disabled :: ReadM a

Null Option reader. All arguments will fail validation.

readerAbort :: ParseError -> ReadM a

Abort option reader by exiting with a ParseError.

readerError :: String -> ReadM a

Abort option reader by exiting with an error message.

Builder for ParserInfo

data InfoMod a

Modifier for ParserInfo.

Instances

Monoid (InfoMod a)

fullDesc :: InfoMod a

Show a full description in the help text of this parser.

briefDesc :: InfoMod a

Only show a brief description in the help text of this parser.

header :: String -> InfoMod a

Specify a header for this parser.

headerDoc :: Maybe Doc -> InfoMod a

Specify a header for this parser as a Doc value.

footer :: String -> InfoMod a

Specify a footer for this parser.

footerDoc :: Maybe Doc -> InfoMod a

Specify a footer for this parser as a Doc value.

progDesc :: String -> InfoMod a

Specify a short program description.

progDescDoc :: Maybe Doc -> InfoMod a

Specify a short program description as a Doc value.

failureCode :: Int -> InfoMod a

Specify an exit code if a parse error occurs.

noIntersperse :: InfoMod a

Disable parsing of regular options after arguments

info :: Parser a -> InfoMod a -> ParserInfo a

Create a ParserInfo given a Parser and a modifier.

Builder for ParserPrefs

data PrefsMod

Instances

Monoid PrefsMod

multiSuffix :: String -> PrefsMod

disambiguate :: PrefsMod

showHelpOnError :: PrefsMod

noBacktrack :: PrefsMod

columns :: Int -> PrefsMod

prefs :: PrefsMod -> ParserPrefs

defaultPrefs :: ParserPrefs

Default preferences.

Types

data Mod f a

An option modifier.

Option modifiers are values that represent a modification of the properties of an option.

The type parameter a is the return type of the option, while f is a record containing its properties (e.g. OptionFields for regular options, FlagFields for flags, etc...).

An option modifier consists of 3 elements:

• A field modifier, of the form f a -> f a. These are essentially (compositions of) setters for some of the properties supported by f.
• An optional default value and function to display it.
• A property modifier, of the form OptProperties -> OptProperties. This is just like the field modifier, but for properties applicable to any option.

Modifiers are instances of Monoid, and can be composed as such.

You rarely need to deal with modifiers directly, as most of the times it is sufficient to pass them to builders (such as strOption or flag) to create options (see Builder).

Instances

Monoid (Mod f a)

data ReadM a

A newtype over 'ReaderT String Except', used by option readers.

Instances

Alternative ReadM

Monad ReadM

Functor ReadM

MonadPlus ReadM

Applicative ReadM

data OptionFields a

Instances

HasMetavar OptionFields

HasValue OptionFields

HasCompleter OptionFields

HasName OptionFields

data FlagFields a

Instances

HasName FlagFields

data ArgumentFields a

Instances

HasMetavar ArgumentFields

HasValue ArgumentFields

HasCompleter ArgumentFields

data CommandFields a

Instances

HasMetavar CommandFields