Copyright	(C) 2012-14 Edward Kmett
License	BSD-style (see the file LICENSE)
Maintainer	Edward Kmett <ekmett@gmail.com>
Stability	experimental
Portability	non-portable
Safe Haskell	Trustworthy
Language	Haskell98

Control.Lens.Action

Contents

Composable Actions
Indexed Actions
Folds with Effects
Implementation Details

Description

Synopsis

Composable Actions

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

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 a Source

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 :: IndexPreservingAction m (m a) a Source

A self-running Action, analogous to join.

acts ≡ act id

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

(1,getLine)^!!_2.acts.folded.to succ aa "bb"

perform :: Monad m => Acting m a s a -> s -> m a Source

Perform an Action.

perform ≡ flip ('^!')

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

Perform an Action and modify the result.

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

liftAct :: (MonadTrans trans, Monad m) => Acting m a s a -> IndexPreservingAction (trans m) s a Source

Apply a Monad transformer to an Action.

(^!) :: Monad m => s -> Acting m a s a -> m a infixr 8 Source

Perform an Action.

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

(^!!) :: Monad m => s -> Acting m [a] s a -> m [a] infixr 8 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"]

1,2: ^!!folded.act (i -> putStr (show i ++ ": ") >> getLine).each.to succ 1: aa 2: bb "bbcc"

(^!?) :: Monad m => s -> Acting m (Leftmost a) s a -> m (Maybe a) infixr 8 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 s Source

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 a Source

Construct an IndexedAction from a monadic side-effect.

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

Perform an IndexedAction.

iperform ≡ flip ('^@!')

iperforms :: Monad m => IndexedActing i m e s a -> (i -> a -> e) -> s -> m e Source

Perform an IndexedAction and modify the result.

(^@!) :: Monad m => s -> IndexedActing i m (i, a) s a -> m (i, a) infixr 8 Source

Perform an IndexedAction.

(^@!!) :: Monad m => s -> IndexedActing i m [(i, a)] s a -> m [(i, a)] infixr 8 Source

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

(^@!?) :: Monad m => s -> IndexedActing i m (Leftmost (i, a)) s a -> m (Maybe (i, a)) infixr 8 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 s Source

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

A MonadicFold can use side-effects to produce parts of the structure being folded (e.g. reading them from file).

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 s Source

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 a = LensLike (Effect m r) s s a a Source

Used to evaluate an Action.

type IndexedActing i m r s a = Over (Indexed i) (Effect m r) s s a a Source

Used to evaluate an IndexedAction.

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

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.

Minimal complete definition

effective, ineffective

Instances

Effective Identity r (Const r)
Monad m => Effective m r (Effect m r)
Effective m r f => Effective m r (AlongsideRight f b)
Effective m r f => Effective m r (AlongsideLeft f b)
Effective m r f => Effective m (Dual r) (Backwards f)