Safe Haskell | Safe |
---|---|

Language | Haskell98 |

This module contains an arrow interface for option parsers, which allows to define and combine parsers using the arrow notation and arrow combinators.

The arrow syntax is particularly useful to create parsers of nested structures, or records where the order of fields is different from the order in which the parsers should be applied.

For example, an `arguments`

parser often needs
to be applied last, and that makes it inconvenient to use it for a field
which is not the last one in a record.

Using the arrow syntax and the functions in this module, one can write, e.g.:

data Options = Options { optArgs :: [String] , optVerbose :: Bool } opts :: Parser Options opts = runA $ proc () -> do verbose <- asA (switch (short 'v')) -< () args <- asA (arguments str idm) -< () returnA -< Options args verbose

Parser arrows, created out of regular `Parser`

values using the `asA`

function, are arrows taking `()`

as argument and returning the parsed value.

- module Control.Arrow
- newtype A f a b = A {
- unA :: f (a -> b)

- asA :: Applicative f => f a -> A f () a
- runA :: Applicative f => A f () a -> f a
- type ParserA = A Parser

# Documentation

module Control.Arrow

For any `Applicative`

functor `f`

, `A f`

is the `Arrow`

instance
associated to `f`

.

The `A`

constructor can be used to convert a value of type `f (a -> b)`

into
an arrow.

Applicative f => Arrow (A f) # | |

Applicative f => Category * (A f) # | |

asA :: Applicative f => f a -> A f () a #

Convert a value of type `f a`

into an arrow taking `()`

as argument.

Applied to a value of type `Parser`

, it turns it into an arrow that can be
used inside an arrow command, or passed to arrow combinators.

runA :: Applicative f => A f () a -> f a #

Convert an arrow back to an applicative value.

This function can be used to return a result of type `Parser`

from an arrow
command.