Options.Applicative.Simple

Generate and execute a simple options parser.

Generate a simple options parser.

Most of the time you should use simpleOptions instead, but simpleParser can be used for sub-commands that need common options. For example:

addCommand "thing"
           "Subcommands that operate on things"
           (\(opts,runSubCmd) -> runSubCmd opts)
           (simpleParser (flag () () (long "some-flag")) $
            do addCommand "delete"
                          "Delete the thing"
                          (const deleteTheThing)
                          (pure ())
               addCommand "create"
                          "Create a thing"
                          createAThing
                          (strOption (long "hello")))

Generate a string like Version 1.2, Git revision 1234.

$(simpleVersion …) :: String

Add a command to the options dispatcher.

Add a command that takes sub-commands to the options dispatcher.

Example:

addSubCommands "thing"
               "Subcommands that operate on things"
               (do addCommand "delete"
                              "Delete the thing"
                              (const deleteTheThing)
                              (pure ())
                   addCommand "create"
                              "Create a thing"
                              createAThing
                              (strOption (long "hello")))

If there are common options between all the sub-commands, use addCommand in combination with simpleParser instead of addSubCommands.

A functor with application, providing operations to

• embed pure expressions (pure), and

• sequence computations and combine their results (<*> and liftA2).

A minimal complete definition must include implementations of pure and of either <*> or liftA2. If it defines both, then they must behave the same as their default definitions:

(<*>) = liftA2 id

liftA2 f x y = f Prelude.<$> x <*> y

Further, any definition must satisfy the following:

Identity

pure id <*> v = v

Composition

pure (.) <*> u <*> v <*> w = u <*> (v <*> w)

Homomorphism

pure f <*> pure x = pure (f x)

Interchange

u <*> pure y = pure ($ y) <*> u

The other methods have the following default definitions, which may be overridden with equivalent specialized implementations:

• u *> v = (id <$ u) <*> v

• u <* v = liftA2 const u v

As a consequence of these laws, the Functor instance for f will satisfy

• fmap f x = pure f <*> x

It may be useful to note that supposing

forall x y. p (q x y) = f x . g y

it follows from the above that

liftA2 p (liftA2 q u v) = liftA2 f u . liftA2 g v

If f is also a Monad, it should satisfy

• pure = return

• m1 <*> m2 = m1 >>= (\x1 -> m2 >>= (\x2 -> return (x1 x2)))

• (*>) = (>>)

(which implies that pure and <*> satisfy the applicative functor laws).

A Parser a is an option parser returning a value of type 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 Options.Applicative.Builder).

The most general way to run a program description in pure code.

Create a ParserPrefs given a modifier

Trivial option modifier.

Result of execParserPure.

Run a program description.

Parse command line arguments. Display help text and exit if any parse error occurs.

Handle ParserResult.

Create a ParserInfo given a Parser and a modifier.

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

Specify a header for this parser.

Specify a short program description.

An option that always fails and displays a message.

Specify a long name for an option.

Specify the help text for an option.

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"))
       )

An infix synonym for fmap.

The name of this operator is an allusion to Prelude.$. Note the similarities between their types:

 ($)  ::              (a -> b) ->   a ->   b
(<$>) :: Functor f => (a -> b) -> f a -> f b

Whereas Prelude.$ is function application, <$> is function application lifted over a Functor.

Examples

Convert from a Maybe Int to a Maybe String using show:

>>> show <$> NothingNothing

>>> show <$> Just 3Just "3"

Convert from an Either Int Int to an Either Int String using show:

>>> show <$> Left 17Left 17

>>> show <$> Right 17Right "17"

Double each element of a list:

>>> (*2) <$> [1,2,3][2,4,6]

Apply even to the second element of a pair:

>>> even <$> (2,2)(2,True)

A hidden "helper" option which always fails.

A common usage pattern is to apply this applicatively when creating a ParserInfo

opts :: ParserInfo Sample
opts = info (sample <**> helper) mempty

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.

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

By default, sub-parsers allow backtracking to their parent's options when they are completed. To allow full mixing of parent and sub-parser options, turn on subparserInline; otherwise, to disable backtracking completely, use noBacktrack.

Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version.

Examples

Perform a computation with Maybe and replace the result with a constant value if it is Just:

>>> 'a' <$ Just 2Just 'a'>>> 'a' <$ NothingNothing

An associative operation

NOTE: This method is redundant and has the default implementation mappend = (<>) since base-4.11.0.0. Should it be implemented manually, since mappend is a synonym for (<>), it is expected that the two functions are defined the same way. In a future GHC release mappend will be removed from Monoid.

A monoid on applicative functors.

If defined, some and many should be the least solutions of the equations:

• some v = (:) Prelude.<$> v <*> many v

• many v = some v <|> pure []

Examples

>>> Nothing <|> Just 42Just 42

>>> [1, 2] <|> [3, 4][1,2,3,4]

>>> empty <|> print (2^15)32768

A variant of <*> with the types of the arguments reversed. It differs from flip (<*>) in that the effects are resolved in the order the arguments are presented.

Examples

>>> (<**>) (print 1) (id <$ print 2)12

>>> flip (<*>) (print 1) (id <$ print 2)21

>>> ZipList [4, 5, 6] <**> ZipList [(+1), (*2), (/3)]ZipList {getZipList = [5.0,10.0,2.0]}

Lift a function to actions. Equivalent to Functor's fmap but implemented using only Applicative's methods: liftA f a = pure f <*> a

As such this function may be used to implement a Functor instance from an Applicative one.

Examples

Using the Applicative instance for Lists:

>>> liftA (+1) [1, 2][2,3]

Or the Applicative instance for Maybe

>>> liftA (+1) (Just 3)Just 4

Lift a ternary function to actions.

String Option reader.

Polymorphic over the IsString type class since 0.14.

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'.

The Const functor.

Examples

>>> fmap (++ "World") (Const "Hello")Const "Hello"

Because we ignore the second type parameter to Const, the Applicative instance, which has (<*>) :: Monoid m => Const m (a -> b) -> Const m a -> Const m b essentially turns into Monoid m => m -> m -> m, which is (<>)

>>> Const [1, 2, 3] <*> Const [4, 5, 6]Const [1,2,3,4,5,6]

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.

Modifier for ParserInfo.

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.

Builder for an argument parser.

Option reader based on the Read type class.

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

Set the maximum width of the generated help text.

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.

Add a list of possible completion values.

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.

Default preferences.

Null Option reader. All arguments will fail validation.

Turn on disambiguation.

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

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)

Specify an exit code if a parse error occurs.

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.

Specify a footer for this parser.

Specify a footer for this parser as a 'Prettyprinter.Doc AnsiStyle' value.

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.

Specify a header for this parser as a 'Prettyprinter.Doc AnsiStyle' value.

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

Set fill width in help text presentation.

Show equals sign, rather than space, in usage and help text for options with long names.

Show global help information in subparser usage.

Hide this option from the brief description.

Use internal to hide the option from the help text too.

Convert a function producing a Maybe into a reader.

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.

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

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

Turn off backtracking after subcommand is parsed.

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.

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' )

Specify a short program description as a 'Prettyprinter.Doc AnsiStyle' value.

Specify a short name for an option.

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

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

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.

Show full help text on any error.

Builder for a String argument.

Builder for an option taking a String argument.

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

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

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

Allow full mixing of subcommand and parent arguments by inlining selected subparsers into the parent parser.

NOTE: When this option is used, preferences for the subparser which effect the parser behaviour (such as noIntersperse) are ignored.

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

Run a compgen 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.

Create a Completer from a constant list of strings.

Create a Completer from an IO action

Hide this option completely from the help text

Use hidden if the option should remain visible in the full description.

Run a program description with custom preferences.

Extract the actual result from a ParserResult value.

This function returns Nothing in case of errors. Possible error messages or completion actions are simply discarded.

If you want to display error messages and invoke completion actions appropriately, use handleParseResult instead.

Builder for a command parser with a "helper" option attached. Used in the same way as subparser, but includes a "--help|-h" inside the subcommand.

Generate a ParserFailure from a ParseError in a given Context.

This function can be used, for example, to show the help text for a parser:

handleParseResult . Failure $ parserFailure pprefs pinfo (ShowHelpText Nothing) mempty

A hidden "--version" option that displays the version.

opts :: ParserInfo Sample
opts = info (sample <**> simpleVersioner "v1.2.3") mempty

A shell complete function.

A full description for a runnable Parser for a program.

Global preferences for a top-level Parser.

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

Smart constructor for a Completer

Abort option reader by exiting with a ParseError.

Abort option reader by exiting with an error message.

One or none.

It is useful for modelling any computation that is allowed to fail.

Examples

Using the Alternative instance of Control.Monad.Except, the following functions:

>>> import Control.Monad.Except

>>> canFail = throwError "it failed" :: Except String Int>>> final = return 42                :: Except String Int

Can be combined by allowing the first function to fail:

>>> runExcept $ canFail *> finalLeft "it failed"

>>> runExcept $ optional canFail *> finalRight 42

The sum of a collection of actions using (<|>), generalizing concat.

asum is just like msum, but generalised to Alternative.

Examples

Basic usage:

>>> asum [Just "Hello", Nothing, Just "World"]Just "Hello"

Lists, but with an Applicative functor based on zipping.

Examples

In contrast to the Applicative for GHC.List.List:

>>> (+) <$> [1, 2, 3] <*> [4, 5, 6][5,6,7,6,7,8,7,8,9]

The Applicative instance of ZipList applies the operation by pairing up the elements, analogous to zipWithN

>>> (+) <$> ZipList [1, 2, 3] <*> ZipList [4, 5, 6]ZipList {getZipList = [5,7,9]}

>>> (,,,) <$> ZipList [1, 2] <*> ZipList [3, 4] <*> ZipList [5, 6] <*> ZipList [7, 8]ZipList {getZipList = [(1,3,5,7),(2,4,6,8)]}

>>> ZipList [(+1), (^2), (/ 2)] <*> ZipList [5, 5, 5]ZipList {getZipList = [6.0,25.0,2.5]}