hxt-9.1.6: A collection of tools for processing XML with Haskell.

Portability | portable
Stability | experimental
Maintainer | Uwe Schmidt (uwe\@fh-wedel.de)

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

- class ArrowList a => ArrowIf a where
  - ifA :: a b c -> a b d -> a b d -> a b d
  - ifP :: (b -> Bool) -> a b d -> a b d -> a b d
  - neg :: a b c -> a b b
  - when :: a b b -> a b c -> a b b
  - whenP :: a b b -> (b -> Bool) -> a b b
  - whenNot :: a b b -> a b c -> a b b
  - whenNotP :: a b b -> (b -> Bool) -> a b b
  - guards :: a b c -> a b d -> a b d
  - guardsP :: (b -> Bool) -> a b d -> a b d
  - filterA :: a b c -> a b b
  - containing :: a b c -> a c d -> a b c
  - notContaining :: a b c -> a c d -> a b c
  - orElse :: a b c -> a b c -> a b c
  - choiceA :: [IfThen (a b c) (a b d)] -> a b d
  - tagA :: a b c -> a b (Either b b)
  - spanA :: a b b -> a [b] ([b], [b])
  - partitionA :: a b b -> a [b] ([b], [b])
- data IfThen a b = a :-> b

# Documentation

class ArrowList a => ArrowIf a where

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 d

if lifted to arrows

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

shortcut: `ifP p = ifA (isA p)`

neg :: a b c -> a b b

negation: `neg f = ifA f none this`

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

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

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

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

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

`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 b

like `whenP`

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

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

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

like `whenP`

filterA :: a b c -> a b b

shortcut for `f `guards` this`

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

`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 c

`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 c

`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 d

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)

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])

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])

partition a list of values into a pair of lists

This is the arrow Version of `partition`

Instances

ArrowIf LA |
ArrowIf IOLA |
ArrowIf (SLA s) |
ArrowIf (IOSLA s) |

data IfThen a b

an auxiliary data type for `choiceA`

Constructors

a :-> b |