lens-3.9.2: Lenses, Folds and Traversals

Portabilitynon-portable
Stabilityexperimental
MaintainerEdward Kmett <ekmett@gmail.com>
Safe HaskellNone

Control.Lens.Action

Contents

Description

 

Synopsis

Composable Actions

type Action m s a = forall f r. Effective m r f => (a -> f a) -> s -> f sSource

An Action is a Getter enriched with access to a Monad for side-effects.

Every Getter can be used as an Action.

You can compose an Action with another Action using (.) from the Prelude.

act :: Monad m => (s -> m a) -> IndexPreservingAction m s aSource

Construct an Action from a monadic side-effect. 

>>> ["hello","world"]^!folded.act (\x -> [x,x ++ "!"])
["helloworld","helloworld!","hello!world","hello!world!"]

 act :: Monad m => (s -> m a) -> Action m s a
 act sma afb a = effective (sma a >>= ineffective . afb)

acts :: Action m (m a) aSource

A self-running Action, analogous to join. 

 acts ≡ act id

>>> (1,"hello")^!_2.acts.to succ
"ifmmp"

perform :: Monad m => Acting m a s t a b -> s -> m aSource

Perform an Action. 

 perform ≡ flip (^!)

performs :: (Profunctor p, Monad m) => Over p (Effect m e) s t a b -> p a e -> s -> m eSource

Perform an Action and modify the result. 

 performs :: Monad m => Acting m e s t a b -> (a -> e) -> s -> m e

liftAct :: (MonadTrans trans, Monad m) => Acting m a s t a b -> Action (trans m) s aSource

Apply a Monad transformer to an Action.

(^!) :: Monad m => s -> Acting m a s t a b -> m aSource

Perform an Action. 

>>> ["hello","world"]^!folded.act putStrLn
hello
world

(^!!) :: Monad m => s -> Acting m [a] s t a b -> m [a]Source

Perform a MonadicFold and collect all of the results in a list. 

>>> ["ab","cd","ef"]^!!folded.acts
["ace","acf","ade","adf","bce","bcf","bde","bdf"]

(^!?) :: Monad m => s -> Acting m (Leftmost a) s t a b -> m (Maybe a)Source

Perform a MonadicFold and collect the leftmost result.

Note: this still causes all effects for all elements. 

>>> [Just 1, Just 2, Just 3]^!?folded.acts
Just (Just 1)
>>> [Just 1, Nothing]^!?folded.acts
Nothing

Indexed Actions

type IndexedAction i m s a = forall p f r. (Indexable i p, Effective m r f) => p a (f a) -> s -> f sSource

An IndexedAction is an IndexedGetter enriched with access to a Monad for side-effects.

Every Getter can be used as an Action.

You can compose an Action with another Action using (.) from the Prelude.

iact :: Monad m => (s -> m (i, a)) -> IndexedAction i m s aSource

Construct an IndexedAction from a monadic side-effect.

iperform :: Monad m => IndexedActing i m (i, a) s t a b -> s -> m (i, a)Source

Perform an IndexedAction. 

 iperform ≡ flip (^@!)

iperforms :: Monad m => IndexedActing i m e s t a b -> (i -> a -> e) -> s -> m eSource

Perform an IndexedAction and modify the result.

(^@!) :: Monad m => s -> IndexedActing i m (i, a) s t a b -> m (i, a)Source

Perform an IndexedAction.

(^@!!) :: Monad m => s -> IndexedActing i m [(i, a)] s t a b -> m [(i, a)]Source

Obtain a list of all of the results of an IndexedMonadicFold.

(^@!?) :: Monad m => s -> IndexedActing i m (Leftmost (i, a)) s t a b -> m (Maybe (i, a))Source

Perform an IndexedMonadicFold and collect the Leftmost result.

Note: this still causes all effects for all elements.

Folds with Effects

type MonadicFold m s a = forall f r. (Effective m r f, Applicative f) => (a -> f a) -> s -> f sSource

A MonadicFold is a Fold enriched with access to a Monad for side-effects.

Every Fold can be used as a MonadicFold, that simply ignores the access to the Monad.

You can compose a MonadicFold with another MonadicFold using (.) from the Prelude.

type IndexedMonadicFold i m s a = forall p f r. (Indexable i p, Effective m r f, Applicative f) => p a (f a) -> s -> f sSource

An IndexedMonadicFold is an IndexedFold enriched with access to a Monad for side-effects.

Every IndexedFold can be used as an IndexedMonadicFold, that simply ignores the access to the Monad.

You can compose an IndexedMonadicFold with another IndexedMonadicFold using (.) from the Prelude.

Implementation Details

type Acting m r s t a b = LensLike (Effect m r) s t a bSource

Used to evaluate an Action.

type IndexedActing i m r s t a b = Over (Indexed i) (Effect m r) s t a bSource

Used to evaluate an IndexedAction.

class (Monad m, Functor f, Contravariant f) => Effective m r f | f -> m rSource

An Effective Functor ignores its argument and is isomorphic to a Monad wrapped around a value.

That said, the Monad is possibly rather unrelated to any Applicative structure.

Instances

Effective Identity r (Accessor r) 
Monad m => Effective m r (Effect m r) 
Effective m r f => Effective m (Dual r) (Backwards f)