Control.Lens.Zoom

Documentation

class (Magnified m ~ Magnified n, MonadReader b m, MonadReader a n) => Magnify m n b a | m -> b, n -> a, m a -> n, n b -> m where

This class allows us to use magnify part of the environment, changing the environment supplied by many different Monad transformers. Unlike zoom this can change the environment of a deeply nested Monad transformer.

Also, unlike zoom, this can be used with any valid Getter, but cannot be used with a Traversal or Fold.

Methods

magnify :: LensLike' (Magnified m c) a b -> m c -> n c infixr 2

Run a monadic action in a larger environment than it was defined in, using a Getter.

This acts like local, but can in many cases change the type of the environment as well.

This is commonly used to lift actions in a simpler Reader Monad into a Monad with a larger environment type.

This can be used to edit pretty much any Monad transformer stack with an environment in it:

>>> (1,2) & magnify _2 (+1)
3

>>> flip Reader.runReader (1,2) $ magnify _1 Reader.ask
1

>>> flip Reader.runReader (1,2,[10..20]) $ magnify (_3._tail) Reader.ask
[11,12,13,14,15,16,17,18,19,20]

magnify :: Getter s a -> (a -> r) -> s -> r
magnify :: Monoid r => Fold s a   -> (a -> r) -> s -> r

magnify :: Monoid w                 => Getter s t -> RWS t w st c -> RWS s w st c
magnify :: (Monoid w, Monoid c) => Fold s a   -> RWS a w st c -> RWS s w st c
...

Instances

Magnify ((->) b) ((->) a) b a

magnify = views

Magnify m n b a => Magnify (IdentityT m) (IdentityT n) b a

Monad m => Magnify (ReaderT b m) (ReaderT a m) b a

(Monad m, Monoid w) => Magnify (RWST b w s m) (RWST a w s m) b a

(Monad m, Monoid w) => Magnify (RWST b w s m) (RWST a w s m) b a

class (Zoomed m ~ Zoomed n, MonadState s m, MonadState t n) => Zoom m n s t | m -> s, n -> t, m t -> n, n s -> m where

This class allows us to use zoom in, changing the State supplied by many different Monad transformers, potentially quite deep in a Monad transformer stack.

Methods

zoom :: LensLike' (Zoomed m c) t s -> m c -> n c infixr 2

Run a monadic action in a larger State than it was defined in, using a Lens' or Traversal'.

This is commonly used to lift actions in a simpler State Monad into a State Monad with a larger State type.

When applied to a Traversal' over multiple values, the actions for each target are executed sequentially and the results are aggregated.

This can be used to edit pretty much any Monad transformer stack with a State in it!

>>> flip State.evalState (a,b) $ zoom _1 $ use id
a

>>> flip State.execState (a,b) $ zoom _1 $ id .= c
(c,b)

>>> flip State.execState [(a,b),(c,d)] $ zoom traverse $ _2 %= f
[(a,f b),(c,f d)]

>>> flip State.runState [(a,b),(c,d)] $ zoom traverse $ _2 <%= f
(f b <> f d <> mempty,[(a,f b),(c,f d)])

>>> flip State.evalState (a,b) $ zoom both (use id)
a <> b

zoom :: Monad m             => Lens' s t      -> StateT t m a -> StateT s m a
zoom :: (Monad m, Monoid c) => Traversal' s t -> StateT t m c -> StateT s m c
zoom :: (Monad m, Monoid w)             => Lens' s t      -> RWST r w t m c -> RWST r w s m c
zoom :: (Monad m, Monoid w, Monoid c) => Traversal' s t -> RWST r w t m c -> RWST r w s m c
zoom :: (Monad m, Monoid w, Error e)  => Lens' s t      -> ErrorT e (RWST r w t m) c -> ErrorT e (RWST r w s m) c
zoom :: (Monad m, Monoid w, Monoid c, Error e) => Traversal' s t -> ErrorT e (RWST r w t m) c -> ErrorT e (RWST r w s m) c
...

Instances

Zoom m n s t => Zoom (IdentityT m) (IdentityT n) s t

Zoom m n s t => Zoom (ListT m) (ListT n) s t

Zoom m n s t => Zoom (MaybeT m) (MaybeT n) s t

Zoom m n s t => Zoom (ReaderT e m) (ReaderT e n) s t

Monad z => Zoom (StateT s z) (StateT t z) s t

Monad z => Zoom (StateT s z) (StateT t z) s t

Zoom m n s t => Zoom (ExceptT e m) (ExceptT e n) s t

(Error e, Zoom m n s t) => Zoom (ErrorT e m) (ErrorT e n) s t

(Monoid w, Zoom m n s t) => Zoom (WriterT w m) (WriterT w n) s t

(Monoid w, Zoom m n s t) => Zoom (WriterT w m) (WriterT w n) s t

(Monoid w, Monad z) => Zoom (RWST r w s z) (RWST r w t z) s t

(Monoid w, Monad z) => Zoom (RWST r w s z) (RWST r w t z) s t