arrow-list-0.6.1: List arrows for Haskell.

Safe HaskellSafe-Inferred

Control.Arrow.ArrowList

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 ar => ArrowList ar whereSource

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.

Methods

arrL :: (a -> [b]) -> a `ar` bSource

mapL :: ([b] -> [c]) -> (a `ar` b) -> a `ar` cSource

Instances

Creating list arrows.

unlist :: ArrowList ar => [b] `ar` bSource

Create a list arrow of an input list.

unite :: ArrowList ar => (a `ar` (b, b)) -> a `ar` bSource

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

none :: ArrowList ar => a `ar` bSource

Ignore the input and produce no results. Like zeroArrow.

concatA :: ArrowPlus ar => [a `ar` b] -> a `ar` bSource

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

Collecting the results.

list :: ArrowList ar => (a `ar` b) -> a `ar` [b]Source

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

empty :: ArrowList ar => (a `ar` b) -> a `ar` BoolSource

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

Conditional and filter arrows.

isA :: ArrowList ar => (a -> Bool) -> a `ar` aSource

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.

ifASource

Arguments

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

Arrow used as condition.

-> (a `ar` b)

Arrow to use when condition has results.

-> (a `ar` b)

Arrow to use when condition has no results.

-> a `ar` 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.

whenSource

Arguments

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

The arrow to apply,

-> (a `ar` b)

when this conditional holds.

-> a `ar` 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

guardsSource

Arguments

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

When this condition holds,

-> (a `ar` b)

then apply this arrow.

-> a `ar` 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 ar, ArrowList ar) => (a `ar` c) -> a `ar` aSource

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 ar, ArrowChoice ar) => (a `ar` c) -> a `ar` aSource

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

orElse :: (ArrowList ar, ArrowChoice ar) => (a `ar` b) -> (a `ar` b) -> a `ar` bSource

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 ar => Maybe a `ar` aSource

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 ar, ArrowList ar) => (a `ar` b) -> a `ar` Maybe bSource

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.