hxt-9.3.1.9: A collection of tools for processing XML with Haskell.

Portabilityportable
Stabilityexperimental
MaintainerUwe Schmidt (uwe\@fh-wedel.de)
Safe HaskellSafe-Inferred

Control.Arrow.ArrowIf

Description

Conditionals for List Arrows

This module defines conditional combinators for list arrows.

The empty list as result represents False, none empty lists True.

Synopsis

Documentation

class ArrowList a => ArrowIf a whereSource

The interface for arrows as conditionals.

Requires list arrows because False is represented as empty list, True as none empty lists.

Only ifA and orElse don't have default implementations

Methods

ifA :: a b c -> a b d -> a b d -> a b dSource

if lifted to arrows

ifP :: (b -> Bool) -> a b d -> a b d -> a b dSource

shortcut: ifP p = ifA (isA p)

neg :: a b c -> a b bSource

negation: neg f = ifA f none this

when :: a b b -> a b c -> a b bSource

f `when` g : when the predicate g holds, f is applied, else the identity filter this

whenP :: a b b -> (b -> Bool) -> a b bSource

shortcut: f `whenP` p = f `when` (isA p)

whenNot :: a b b -> a b c -> a b bSource

f `whenNot` g : when the predicate g does not hold, f is applied, else the identity filter this

whenNotP :: a b b -> (b -> Bool) -> a b bSource

like whenP

guards :: a b c -> a b d -> a b dSource

g `guards` f : when the predicate g holds, f is applied, else none

guardsP :: (b -> Bool) -> a b d -> a b dSource

like whenP

filterA :: a b c -> a b bSource

shortcut for f guards this

containing :: a b c -> a c d -> a b cSource

f `containing` g : keep only those results from f for which g holds

definition: f `containing` g = f >>> g `guards` this

notContaining :: a b c -> a c d -> a b cSource

f `notContaining` g : keep only those results from f for which g does not hold

definition: f `notContaining` g = f >>> ifA g none this

orElse :: a b c -> a b c -> a b cSource

f `orElse` g : directional choice: if f succeeds, the result of f is the result, else g is applied

choiceA :: [IfThen (a b c) (a b d)] -> a b dSource

generalisation of orElse for multi way branches like in case expressions.

An auxiliary data type IfThen with an infix constructor :-> is used for writing multi way branches

example: choiceA [ p1 :-> e1, p2 :-> e2, this :-> default ]

tagA :: a b c -> a b (Either b b)Source

tag a value with Left or Right, if arrow has success, input is tagged with Left, else with Right

spanA :: a b b -> a [b] ([b], [b])Source

split a list value with an arrow and returns a pair of lists. This is the arrow version of span. The arrow is deterministic.

example: runLA (spanA (isA (/= '-'))) "abc-def" gives [("abc","-def")] as result

partitionA :: a b b -> a [b] ([b], [b])Source

partition a list of values into a pair of lists

This is the arrow Version of partition

Instances

data IfThen a b Source

an auxiliary data type for choiceA

Constructors

a :-> b