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 :: IsString s => Mod ArgumentFields s -> Parser s

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.

Note: Because this parser will never fail, it can not be used with combinators such as some or many, as these combinators continue until a failure occurs. See flag'.

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, alternatively

flag' True (long "on") <|> flag' False (long "off")

will require the user to enter '--on' or '--off' on the command line.

switch :: Mod FlagFields Bool -> Parser Bool

Builder for a boolean flag.

Note: Because this parser will never fail, it can not be used with combinators such as some or many, as these combinators continue until a failure occurs. See 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 :: IsString s => Mod OptionFields s -> Parser s

Builder for an option taking a String argument.

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

Builder for an option using the given reader.

This is a regular option, and should always have either a long or short name specified in the modifiers (or both).

nameParser = option str ( long "name" <> short 'n' )

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.

To display the default value, combine with showDefault or showDefaultWith.

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.

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 IsCmdStart SomeParser

ExpectsArgError String

UnexpectedError String SomeParser

Instances

Semigroup ParseError

Methods

(<>) :: ParseError -> ParseError -> ParseError

sconcat :: NonEmpty ParseError -> ParseError

stimes :: Integral b => b -> ParseError -> ParseError

Monoid ParseError

Methods

mempty :: ParseError

mappend :: ParseError -> ParseError -> ParseError

mconcat :: [ParseError] -> ParseError

hidden :: Mod f a

Hide this option from the brief description.

internal :: Mod f a

Hide this option from the help text

style :: (Doc -> Doc) -> Mod f a

Apply a function to the option description in the usage text.

import Options.Applicative.Help
flag' () (short 't' <> style bold)

NOTE: This builder is more flexible than its name and example allude. One of the motivating examples for its addition was to used const to completely replace the usage text of an option.

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

Add a command to a subparser option.

Suggested usage for multiple commands is to add them to a single subparser. e.g.

sample :: Parser Sample
sample = subparser
       ( command "hello"
         (info hello (progDesc "Print greeting"))
      <> command "goodbye"
         (info goodbye (progDesc "Say goodbye"))
       )

commandGroup :: String -> Mod CommandFields a

Add a description to a group of commands.

Advanced feature for separating logical groups of commands on the parse line.

If using the same metavar for each group of commands, it may yield a more attractive usage text combined with hidden for some groups.

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.

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 :: IsString s => ReadM s

String Option reader.

Polymorphic over the IsString type class since 0.14.

maybeReader :: (String -> Maybe a) -> ReadM a

Convert a function producing a Maybe into a reader.

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

Convert a function producing an Either into a reader.

As an example, one can create a ReadM from an attoparsec Parser easily with

import qualified Data.Attoparsec.Text as A
import qualified Data.Text as T
attoparsecReader :: A.Parser a => ReadM a
attoparsecReader p = eitherReader (A.parseOnly p . T.pack)

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

Semigroup (InfoMod a)

Methods

(<>) :: InfoMod a -> InfoMod a -> InfoMod a

sconcat :: NonEmpty (InfoMod a) -> InfoMod a

stimes :: Integral b => b -> InfoMod a -> InfoMod a

Monoid (InfoMod a)

Methods

mempty :: InfoMod a

mappend :: InfoMod a -> InfoMod a -> InfoMod a

mconcat :: [InfoMod a] -> 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. After a positional argument is parsed, all remaining options and arguments will be treated as a positional arguments. Not recommended in general as users often expect to be able to freely intersperse regular options and flags within command line options.

forwardOptions :: InfoMod a

Intersperse matched options and arguments normally, but allow unmatched options to be treated as positional arguments. This is sometimes useful if one is wrapping a third party cli tool and needs to pass options through, while also providing a handful of their own options. Not recommended in general as typos by the user may not yield a parse error and cause confusion.

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

Create a ParserInfo given a Parser and a modifier.

Builder for ParserPrefs

data PrefsMod

Instances

Semigroup PrefsMod

Methods

(<>) :: PrefsMod -> PrefsMod -> PrefsMod

sconcat :: NonEmpty PrefsMod -> PrefsMod

stimes :: Integral b => b -> PrefsMod -> PrefsMod

Monoid PrefsMod

Methods

mempty :: PrefsMod

mappend :: PrefsMod -> PrefsMod -> PrefsMod

mconcat :: [PrefsMod] -> PrefsMod

multiSuffix :: String -> PrefsMod

Include a suffix to attach to the metavar when multiple values can be entered.

disambiguate :: PrefsMod

Turn on disambiguation.

See https://github.com/pcapriotti/optparse-applicative#disambiguation

showHelpOnError :: PrefsMod

Show full help text on any error.

showHelpOnEmpty :: PrefsMod

Show the help text if the user enters only the program name or subcommand.

This will suppress a Missing: error and show the full usage instead if a user just types the name of the program.

noBacktrack :: PrefsMod

Turn off backtracking after subcommand is parsed.

columns :: Int -> PrefsMod

Set the maximum width of the generated help text.

prefs :: PrefsMod -> ParserPrefs

Create a ParserPrefs given a modifier

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.

One rarely needs 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

Semigroup (Mod f a)

Methods

(<>) :: Mod f a -> Mod f a -> Mod f a

sconcat :: NonEmpty (Mod f a) -> Mod f a

stimes :: Integral b => b -> Mod f a -> Mod f a

Monoid (Mod f a)

Methods

mempty :: Mod f a

mappend :: Mod f a -> Mod f a -> Mod f a

mconcat :: [Mod f a] -> Mod f a

data ReadM a

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

Instances

Monad ReadM

Methods

(>>=) :: ReadM a -> (a -> ReadM b) -> ReadM b

(>>) :: ReadM a -> ReadM b -> ReadM b

return :: a -> ReadM a

fail :: String -> ReadM a

Functor ReadM

Methods

fmap :: (a -> b) -> ReadM a -> ReadM b

(<$) :: a -> ReadM b -> ReadM a

MonadFail ReadM

Methods

fail :: String -> ReadM a

Applicative ReadM

Methods

pure :: a -> ReadM a

(<*>) :: ReadM (a -> b) -> ReadM a -> ReadM b

(*>) :: ReadM a -> ReadM b -> ReadM b

(<*) :: ReadM a -> ReadM b -> ReadM a

Alternative ReadM

Methods

empty :: ReadM a

(<|>) :: ReadM a -> ReadM a -> ReadM a

some :: ReadM a -> ReadM [a]

many :: ReadM a -> ReadM [a]

MonadPlus ReadM

Methods

mzero :: ReadM a

mplus :: ReadM a -> ReadM a -> ReadM a

data OptionFields a

Instances

HasMetavar OptionFields

Methods

hasMetavarDummy :: OptionFields a -> ()

HasValue OptionFields

Methods

hasValueDummy :: OptionFields a -> ()

HasCompleter OptionFields

Methods

modCompleter :: (Completer -> Completer) -> OptionFields a -> OptionFields a

HasName OptionFields

Methods

name :: OptName -> OptionFields a -> OptionFields a

data FlagFields a

Instances

HasName FlagFields

Methods

name :: OptName -> FlagFields a -> FlagFields a

data ArgumentFields a

Instances

HasMetavar ArgumentFields

Methods

hasMetavarDummy :: ArgumentFields a -> ()

HasValue ArgumentFields

Methods

hasValueDummy :: ArgumentFields a -> ()

HasCompleter ArgumentFields

Methods

modCompleter :: (Completer -> Completer) -> ArgumentFields a -> ArgumentFields a

data CommandFields a

Instances

HasMetavar CommandFields

Methods

hasMetavarDummy :: CommandFields a -> ()