Safe Haskell | None |
---|---|

Language | Haskell2010 |

## Synopsis

- data Focus element m result = Focus (m (result, Change element)) (element -> m (result, Change element))
- data Change a
- member :: Monad m => Focus a m Bool
- lookup :: Monad m => Focus a m (Maybe a)
- lookupWithDefault :: Monad m => a -> Focus a m a
- delete :: Monad m => Focus a m ()
- lookupAndDelete :: Monad m => Focus a m (Maybe a)
- insert :: Monad m => a -> Focus a m ()
- insertOrMerge :: Monad m => (a -> a -> a) -> a -> Focus a m ()
- alter :: Monad m => (Maybe a -> Maybe a) -> Focus a m ()
- adjust :: Monad m => (a -> a) -> Focus a m ()
- update :: Monad m => (a -> Maybe a) -> Focus a m ()
- cases :: Monad m => (b, Change a) -> (a -> (b, Change a)) -> Focus a m b
- unitCases :: Monad m => Change a -> (a -> Change a) -> Focus a m ()
- lookupWithDefaultM :: Monad m => m a -> Focus a m a
- insertM :: Monad m => m a -> Focus a m ()
- insertOrMergeM :: Monad m => (a -> a -> m a) -> m a -> Focus a m ()
- alterM :: Monad m => (Maybe a -> m (Maybe a)) -> Focus a m ()
- adjustM :: Monad m => (a -> m a) -> Focus a m ()
- updateM :: Monad m => (a -> m (Maybe a)) -> Focus a m ()
- casesM :: Monad m => m (b, Change a) -> (a -> m (b, Change a)) -> Focus a m b
- unitCasesM :: Monad m => m (Change a) -> (a -> m (Change a)) -> Focus a m ()
- mappingInput :: Monad m => (a -> b) -> (b -> a) -> Focus a m x -> Focus b m x
- extractingInput :: Monad m => Focus a m b -> Focus a m (b, Maybe a)
- extractingChange :: Monad m => Focus a m b -> Focus a m (b, Change a)
- projectingChange :: Monad m => (Change a -> c) -> Focus a m b -> Focus a m (b, c)
- testingIfModifies :: Monad m => Focus a m b -> Focus a m (b, Bool)
- testingIfRemoves :: Monad m => Focus a m b -> Focus a m (b, Bool)
- testingIfInserts :: Monad m => Focus a m b -> Focus a m (b, Bool)
- testingSizeChange :: Monad m => sizeChange -> sizeChange -> sizeChange -> Focus a m b -> Focus a m (b, sizeChange)
- onTVarValue :: Focus a STM b -> Focus (TVar a) STM b

# Documentation

data Focus element m result Source #

Abstraction over the modification of an element of a datastructure.

It is composable using the standard typeclasses, e.g.:

lookupAndDelete :: Monad m => Focus a m (Maybe a) lookupAndDelete = lookup <* delete

## Instances

MonadTrans (Focus element) Source # | |

Monad m => Monad (Focus element m) Source # | |

Functor m => Functor (Focus element m) Source # | |

Monad m => Applicative (Focus element m) Source # | |

Defined in Focus pure :: a -> Focus element m a # (<*>) :: Focus element m (a -> b) -> Focus element m a -> Focus element m b # liftA2 :: (a -> b -> c) -> Focus element m a -> Focus element m b -> Focus element m c # (*>) :: Focus element m a -> Focus element m b -> Focus element m b # (<*) :: Focus element m a -> Focus element m b -> Focus element m a # |

What to do with the focused value.

The interpretation of the commands is up to the context APIs.

# Pure functions

## Reading functions

lookupWithDefault :: Monad m => a -> Focus a m a Source #

Reproduces the behaviour of
`Data.Map.findWithDefault`

with a better name.

## Modifying functions

insertOrMerge :: Monad m => (a -> a -> a) -> a -> Focus a m () Source #

Reproduces the behaviour of
`Data.Map.insertWith`

with a better name.

alter :: Monad m => (Maybe a -> Maybe a) -> Focus a m () Source #

Reproduces the behaviour of
`Data.Map.alter`

.

update :: Monad m => (a -> Maybe a) -> Focus a m () Source #

Reproduces the behaviour of
`Data.Map.update`

.

## Construction utils

cases :: Monad m => (b, Change a) -> (a -> (b, Change a)) -> Focus a m b Source #

Lift pure functions which handle the cases of presence and absence of the element.

unitCases :: Monad m => Change a -> (a -> Change a) -> Focus a m () Source #

Lift pure functions which handle the cases of presence and absence of the element and produce no result.

# Monadic functions

## Reading functions

lookupWithDefaultM :: Monad m => m a -> Focus a m a Source #

A monadic version of `lookupWithDefault`

.

## Modifying functions

insertOrMergeM :: Monad m => (a -> a -> m a) -> m a -> Focus a m () Source #

A monadic version of `insertOrMerge`

.

## Construction utils

casesM :: Monad m => m (b, Change a) -> (a -> m (b, Change a)) -> Focus a m b Source #

Lift monadic functions which handle the cases of presence and absence of the element.

unitCasesM :: Monad m => m (Change a) -> (a -> m (Change a)) -> Focus a m () Source #

Lift monadic functions which handle the cases of presence and absence of the element and produce no result.

# Composition

mappingInput :: Monad m => (a -> b) -> (b -> a) -> Focus a m x -> Focus b m x Source #

Map the Focus input.

# Change-inspecting functions

extractingInput :: Monad m => Focus a m b -> Focus a m (b, Maybe a) Source #

Extends the output with the input.

extractingChange :: Monad m => Focus a m b -> Focus a m (b, Change a) Source #

Extends the output with the change performed.

projectingChange :: Monad m => (Change a -> c) -> Focus a m b -> Focus a m (b, c) Source #

Extends the output with a projection on the change that was performed.

testingIfModifies :: Monad m => Focus a m b -> Focus a m (b, Bool) Source #

Extends the output with a flag,
signaling whether a change, which is not `Leave`

, has been introduced.

testingIfRemoves :: Monad m => Focus a m b -> Focus a m (b, Bool) Source #

Extends the output with a flag,
signaling whether the `Remove`

change has been introduced.

testingIfInserts :: Monad m => Focus a m b -> Focus a m (b, Bool) Source #

Extends the output with a flag,
signaling whether an item will be inserted.
That is, it didn't exist before and a `Set`

change is introduced.

:: Monad m | |

=> sizeChange | Decreased |

-> sizeChange | Didn't change |

-> sizeChange | Increased |

-> Focus a m b | |

-> Focus a m (b, sizeChange) |

Extend the output with a flag, signaling how the size will be affected by the change.