arrow-list-0.7: List arrows for Haskell.

Safe HaskellSafe
LanguageHaskell98

Control.Arrow.List.Class

Contents

Description

The ArrowList type class, and a collection of list arrow related functions. This typeclass can be used to embed functions producing multiple outputs into a an arrow.

Synopsis

ArrowList type class.

class Arrow arr => ArrowList arr where #

The ArrowList class represents two possible actions:

  1. Lifting functions from one value to a list of values into a list arrow.
  2. Mapping a function over the result list of a list arrow.

Minimal complete definition

arrL, mapL

Methods

arrL :: (a -> [b]) -> a `arr` b #

mapL :: ([b] -> [c]) -> (a `arr` b) -> a `arr` c #

Instances

Monad m => ArrowList (ListTArrow m) # 

Methods

arrL :: (a -> [b]) -> ListTArrow m a b #

mapL :: ([b] -> [c]) -> ListTArrow m a b -> ListTArrow m a c #

Creating list arrows.

unlist :: ArrowList arr => [b] `arr` b #

Create a list arrow of an input list.

unite :: ArrowList arr => (a `arr` (b, b)) -> a `arr` b #

Take the output of an arrow producing two results and concatenate them into the result of the list arrow.

none :: ArrowList arr => a `arr` b #

Ignore the input and produce no results. Like zeroArrow.

concatA :: ArrowPlus arr => [a `arr` b] -> a `arr` b #

Collect the results of applying multiple arrows to the same input.

Collecting the results.

list :: ArrowList arr => (a `arr` b) -> a `arr` [b] #

Collect the entire results of an list arrow as a singleton value in the result list.

empty :: ArrowList arr => (a `arr` b) -> a `arr` Bool #

Returns a Bool indicating whether the input arrow produce any results.

Conditional and filter arrows.

isA :: ArrowList arr => (a -> Bool) -> a `arr` a #

Create a filtering list arrow by mapping a predicate function over the input. When the predicate returns True the input will be returned in the output list, when False the empty list is returned.

ifA #

Arguments

:: (ArrowList arr, ArrowChoice arr) 
=> (a `arr` c)

Arrow used as condition.

-> (a `arr` b)

Arrow to use when condition has results.

-> (a `arr` b)

Arrow to use when condition has no results.

-> a `arr` b 

Use the result a list arrow as a conditional, like an if-then-else arrow. When the first arrow produces any results the then arrow will be used, when the first arrow produces no results the else arrow will be used.

when infix 8 #

Arguments

:: (ArrowList arr, ArrowChoice arr) 
=> (a `arr` a)

The arrow to apply,

-> (a `arr` b)

when this conditional holds.

-> a `arr` a 

Apply a list arrow only when a conditional arrow produces any results. When the conditional produces no results the output arrow behaves like the identity. The second input arrow is used as the conditional, this allow you to write: a `when` c

guards infix 8 #

Arguments

:: (ArrowList arr, ArrowChoice arr) 
=> (a `arr` c)

When this condition holds,

-> (a `arr` b)

then apply this arrow.

-> a `arr` b 

Apply a list arrow only when a conditional arrow produces any results. When the conditional produces no results the output arrow produces no results. The first input arrow is used as the conditional, this allow you to write: c `guards` a

filterA :: (ArrowChoice arr, ArrowList arr) => (a `arr` c) -> a `arr` a #

Filter the results of an arrow with a predicate arrow, when the filter condition produces results the input is accepted otherwise it is excluded.

notA :: (ArrowList arr, ArrowChoice arr) => (a `arr` c) -> a `arr` a #

Negation list arrow. Only accept the input when the condition produces no output.

orElse :: (ArrowList arr, ArrowChoice arr) => (a `arr` b) -> (a `arr` b) -> a `arr` b infix 8 #

Apply the input arrow, when the arrow does not produces any results the second fallback arrow is applied. Likely written infix like this a `orElse` b

Optionality.

maybeL :: ArrowList arr => Maybe a `arr` a #

Map a Maybe input to a list output. When the Maybe is a Nothing an empty list will be returned, Just will result in a singleton list.

optional :: (ArrowChoice arr, ArrowList arr) => (a `arr` b) -> a `arr` Maybe b #

Apply a list arrow, when there are no results a Nothing will be returned, otherwise the results will be wrapped in a Just. This function always produces result.