Safe Haskell	None
Language	Haskell2010

Focus

Contents

Pure functions
Monadic functions
Composition
Change-inspecting functions
STM

Synopsis

data Focus element m result = Focus (m (result, Change element)) (element -> m (result, Change element))
data Change a
- = Leave
- | Remove
- | Set 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 ()
accessAndAdjust :: Monad m => (s -> a) -> (s -> s) -> Focus s m (Maybe a)
liftState :: Monad m => State s a -> Focus s m (Maybe a)
liftStateFn :: Monad m => (s -> (a, s)) -> Focus s m (Maybe a)
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

Constructors

Focus (m (result, Change element)) (element -> m (result, Change element))

Instances

Instances details

MonadTrans (Focus element) Source #
Instance details Defined in Focus Methods lift :: Monad m => m a -> Focus element m a #
Monad m => Monad (Focus element m) Source #
Instance details Defined in Focus Methods (>>=) :: Focus element m a -> (a -> Focus element m b) -> Focus element m b # (>>) :: Focus element m a -> Focus element m b -> Focus element m b # return :: a -> Focus element m a #
Functor m => Functor (Focus element m) Source #
Instance details Defined in Focus Methods fmap :: (a -> b) -> Focus element m a -> Focus element m b # (<$) :: a -> Focus element m b -> Focus element m a #
Monad m => Applicative (Focus element m) Source #
Instance details Defined in Focus Methods 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 #

data Change a Source #

What to do with the focused value.

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

Constructors

Leave	Produce no changes
Remove	Delete it
Set a	Set its value to the provided one

Instances

Instances details

Functor Change Source #
Instance details Defined in Focus Methods fmap :: (a -> b) -> Change a -> Change b # (<$) :: a -> Change b -> Change a #
Eq a => Eq (Change a) Source #
Instance details Defined in Focus Methods (==) :: Change a -> Change a -> Bool # (/=) :: Change a -> Change a -> Bool #
Ord a => Ord (Change a) Source #
Instance details Defined in Focus Methods compare :: Change a -> Change a -> Ordering # (<) :: Change a -> Change a -> Bool # (<=) :: Change a -> Change a -> Bool # (>) :: Change a -> Change a -> Bool # (>=) :: Change a -> Change a -> Bool # max :: Change a -> Change a -> Change a # min :: Change a -> Change a -> Change a #
Show a => Show (Change a) Source #
Instance details Defined in Focus Methods showsPrec :: Int -> Change a -> ShowS # show :: Change a -> String # showList :: [Change a] -> ShowS #
Semigroup (Change a) Source #
Instance details Defined in Focus Methods (<>) :: Change a -> Change a -> Change a # sconcat :: NonEmpty (Change a) -> Change a # stimes :: Integral b => b -> Change a -> Change a #
Monoid (Change a) Source #
Instance details Defined in Focus Methods mempty :: Change a # mappend :: Change a -> Change a -> Change a # mconcat :: [Change a] -> Change a #

Pure functions

Reading functions

member :: Monad m => Focus a m Bool Source #

Reproduces the behaviour of Data.Map.member.

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

Reproduces the behaviour of Data.Map.lookup.

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

Reproduces the behaviour of Data.Map.findWithDefault with a better name.

Modifying functions

delete :: Monad m => Focus a m () Source #

Reproduces the behaviour of Data.Map.delete.

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

Lookup an element and delete it if it exists.

Same as lookup <* delete.

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

Reproduces the behaviour of Data.Map.insert.

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.

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

Reproduces the behaviour of Data.Map.adjust.

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

Reproduces the behaviour of Data.Map.update.

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

Same as all of the following expressions:

f g -> fmap (fmap f) lookup <* adjust g f g -> liftStateFn (f &&& g) f g -> liftStateFn ((,) $ f * g)

liftState :: Monad m => State s a -> Focus s m (Maybe a) Source #

Lift a pure state monad.

liftStateFn :: Monad m => (s -> (a, s)) -> Focus s m (Maybe a) Source #

Lift a pure state-monad-like function.

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

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

A monadic version of insert.

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

A monadic version of insertOrMerge.

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

A monadic version of alter.

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

A monadic version of adjust.

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

A monadic version of update.

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.

testingSizeChange Source #

Arguments

:: 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.

STM

onTVarValue :: Focus a STM b -> Focus (TVar a) STM b Source #

Focus on the contents of a TVar.