Focus · focus-1.0.3.2 · horizon-platform

datadata Focus element (m :: Type -> Type) result

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))

Instances4MonadTrans, Monad, Functor, Applicative

MonadTrans (Focus element)Defined in focus-1.0.3.2 · Focus
Monad m => Monad (Focus element m)Defined in focus-1.0.3.2 · Focus
Functor m => Functor (Focus element m)Defined in focus-1.0.3.2 · Focus
Monad m => Applicative (Focus element m)Defined in focus-1.0.3.2 · Focus

datadata Change a

#

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

Instances6Functor, Eq, Ord, Show, Semigroup, Monoid

Functor ChangeDefined in focus-1.0.3.2 · Focus
Eq a => Eq (Change a)Defined in focus-1.0.3.2 · Focus
Ord a => Ord (Change a)Defined in focus-1.0.3.2 · Focus
Show a => Show (Change a)Defined in focus-1.0.3.2 · Focus
Semigroup (Change a)Defined in focus-1.0.3.2 · Focus
Monoid (Change a)Defined in focus-1.0.3.2 · Focus

Pure functions

0 declarations

Reading functions

valuemember :: Monad m => Focus a m Bool

#

Reproduces the behaviour of Data.Map.member.

valuelookup :: Monad m => Focus a m (Maybe a)

#

Reproduces the behaviour of Data.Map.lookup.

valuelookupWithDefault :: Monad m => a -> Focus a m a

#

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

Modifying functions

valuedelete :: Monad m => Focus a m ()

#

Reproduces the behaviour of Data.Map.delete.

valuelookupAndDelete :: Monad m => Focus a m (Maybe a)

#

Lookup an element and delete it if it exists.

Same as lookup <* delete.

valueinsert :: Monad m => a -> Focus a m ()

#

Reproduces the behaviour of Data.Map.insert.

valueinsertOrMerge :: Monad m => (a -> a -> a) -> a -> Focus a m ()

#

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

valuealter :: Monad m => (Maybe a -> Maybe a) -> Focus a m ()

#

Reproduces the behaviour of Data.Map.alter.

valueadjust :: Monad m => (a -> a) -> Focus a m ()

#

Reproduces the behaviour of Data.Map.adjust.

valueupdate :: Monad m => (a -> Maybe a) -> Focus a m ()

#

Reproduces the behaviour of Data.Map.update.

valueaccessAndAdjust :: Monad m => (s -> a) -> (s -> s) -> Focus s m (Maybe a)

#

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)

valueliftState :: Monad m => State s a -> Focus s m (Maybe a)

#

Lift a pure state monad.

valueliftStateFn :: Monad m => (s -> (a, s)) -> Focus s m (Maybe a)

#

Lift a pure state-monad-like function.

Construction utils

valuecases :: Monad m => (b, Change a) -> (a -> (b, Change a)) -> Focus a m b

#

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

valueunitCases :: Monad m => Change a -> (a -> Change a) -> Focus a m ()

#

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

Monadic functions

0 declarations

Reading functions

valuelookupWithDefaultM :: Monad m => m a -> Focus a m a

#

A monadic version of lookupWithDefault.

Modifying functions

valueinsertM :: Monad m => m a -> Focus a m ()

#

A monadic version of insert.

valueinsertOrMergeM :: Monad m => (a -> a -> m a) -> m a -> Focus a m ()

#

A monadic version of insertOrMerge.

valuealterM :: Monad m => (Maybe a -> m (Maybe a)) -> Focus a m ()

#

A monadic version of alter.

valueadjustM :: Monad m => (a -> m a) -> Focus a m ()

#

A monadic version of adjust.

valueupdateM :: Monad m => (a -> m (Maybe a)) -> Focus a m ()

#

A monadic version of update.

Construction utils

valuecasesM :: m (b, Change a) -> (a -> m (b, Change a)) -> Focus a m b

#

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

valueunitCasesM :: Monad m => m (Change a) -> (a -> m (Change a)) -> Focus a m ()

#

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

Composition

1 declaration

valuemappingInput

:: Monad m
=> a -> b
-> b -> a
-> Focus a m x
-> Focus b m x

#

Map the Focus input.

Change-inspecting functions

7 declarations

valueextractingInput :: Monad m => Focus a m b -> Focus a m (b, Maybe a)

#

Extends the output with the input.

valueextractingChange :: Monad m => Focus a m b -> Focus a m (b, Change a)

#

Extends the output with the change performed.

valueprojectingChange

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

#

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

valuetestingIfModifies :: Monad m => Focus a m b -> Focus a m (b, Bool)

#

Extends the output with a flag, signaling whether a change, which is not Leave, has been introduced.

valuetestingIfRemoves :: Monad m => Focus a m b -> Focus a m (b, Bool)

#

Extends the output with a flag, signaling whether the Remove change has been introduced.

valuetestingIfInserts :: Monad m => Focus a m b -> Focus a m (b, Bool)

#

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.

valuetestingSizeChange

:: 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

1 declaration

valueonTVarValue :: Focus a STM b -> Focus (TVar a) STM b

#

Focus on the contents of a TVar.