lens-4.0.5: Lenses, Folds and Traversals

PortabilityRank2, MPTCs, fundeps
Stabilityexperimental
MaintainerEdward Kmett <ekmett@gmail.com>
Safe HaskellTrustworthy

Control.Lens.Wrapped

Contents

Description

The Wrapped class provides similar functionality as Control.Newtype, from the newtype package, but in a more convenient and efficient form.

There are a few functions from newtype that are not provided here, because they can be done with the Iso directly: 

 Control.Newtype.over Sum f ≡ _Unwrapping Sum %~ f
 Control.Newtype.under Sum f ≡ _Wrapping Sum %~ f
 Control.Newtype.overF Sum f ≡ mapping (_Unwrapping Sum) %~ f
 Control.Newtype.underF Sum f ≡ mapping (_Wrapping Sum) %~ f

under can also be used with _Unwrapping to provide the equivalent of Control.Newtype.under. Also, most use cases don't need full polymorphism, so only the single constructor _Wrapping functions would be needed.

These equivalences aren't 100% honest, because newtype's operators need to rely on two Newtype constraints. This means that the wrapper used for the output is not necessarily the same as the input.

Synopsis

Wrapping and Unwrapping monomorphically

class Wrapped s whereSource

Wrapped provides isomorphisms to wrap and unwrap newtypes or data types with one constructor.

Associated Types

type Unwrapped s :: *Source

Methods

_Wrapped' :: Iso' s (Unwrapped s)Source

An isomorphism between s and a.

Instances

_Unwrapped' :: Wrapped s => Iso' (Unwrapped s) sSource

_Wrapping' :: Wrapped s => (Unwrapped s -> s) -> Iso' s (Unwrapped s)Source

This is a convenient version of _Wrapped with an argument that's ignored.

The user supplied function is ignored, merely its type is used.

_Unwrapping' :: Wrapped s => (Unwrapped s -> s) -> Iso' (Unwrapped s) sSource

This is a convenient version of _Wrapped with an argument that's ignored.

The user supplied function is ignored, merely its type is used.

Wrapping and unwrapping polymorphically

class Wrapped s => Rewrapped s t Source

Instances

~ * t PatternMatchFail => Rewrapped PatternMatchFail t 
~ * t RecSelError => Rewrapped RecSelError t 
~ * t RecConError => Rewrapped RecConError t 
~ * t RecUpdError => Rewrapped RecUpdError t 
~ * t NoMethodError => Rewrapped NoMethodError t 
~ * t AssertionFailed => Rewrapped AssertionFailed t 
~ * t All => Rewrapped All t 
~ * t Any => Rewrapped Any t 
~ * t ErrorCall => Rewrapped ErrorCall t 
~ * t IntSet => Rewrapped IntSet t

Use wrapping fromList. unwrapping returns a sorted list.

~ * t (ZipList b) => Rewrapped (ZipList a) t 
~ * t (Dual b) => Rewrapped (Dual a) t 
~ * t (Endo b) => Rewrapped (Endo b) t 
~ * t (Sum b) => Rewrapped (Sum a) t 
~ * t (Product b) => Rewrapped (Product a) t 
~ * t (First b) => Rewrapped (First a) t 
~ * t (Last b) => Rewrapped (Last b) t 
~ * t (Identity b) => Rewrapped (Identity a) t 
~ * t (Seq a') => Rewrapped (Seq a) t 
~ * t (IntMap a') => Rewrapped (IntMap a) t

Use wrapping fromList. unwrapping returns a sorted list.

(~ * t (Set a'), Ord a) => Rewrapped (Set a) t

Use wrapping fromList. unwrapping returns a sorted list.

~ * t (Predicate b) => Rewrapped (Predicate a) t 
~ * t (Comparison b) => Rewrapped (Comparison a) t 
~ * t (Equivalence b) => Rewrapped (Equivalence a) t 
~ * t (Min b) => Rewrapped (Min a) t 
~ * t (Max b) => Rewrapped (Max a) t 
~ * t (First b) => Rewrapped (First a) t 
~ * t (Last b) => Rewrapped (Last a) t 
~ * t (WrappedMonoid b) => Rewrapped (WrappedMonoid a) t 
~ * t (Option b) => Rewrapped (Option a) t 
(~ * t (HashSet a'), Hashable a, Eq a) => Rewrapped (HashSet a) t

Use wrapping fromList. Unwrapping returns some permutation of the list.

(~ * t (HashMap k' a'), Hashable k, Eq k) => Rewrapped (HashMap k a) t

Use wrapping fromList. Unwrapping returns some permutation of the list.

(~ * t (Map k' a'), Ord k) => Rewrapped (Map k a) t

Use wrapping fromList. unwrapping returns a sorted list.

~ * t (Const a' x') => Rewrapped (Const a x) t 
~ * t (WrappedMonad m' a') => Rewrapped (WrappedMonad m a) t 
(~ * t (ArrowMonad m' a'), ArrowApply m, ArrowApply m') => Rewrapped (ArrowMonad m a) t 
~ * t (IdentityT n b) => Rewrapped (IdentityT m a) t 
~ * t (Op a' b') => Rewrapped (Op a b) t 
~ * t (ListT n b) => Rewrapped (ListT m a) t 
~ * t (Reverse g b) => Rewrapped (Reverse f a) t 
~ * t (Backwards g b) => Rewrapped (Backwards f a) t 
~ * t (Constant a' b') => Rewrapped (Constant a b) t 
~ * t (MaybeT n b) => Rewrapped (MaybeT m a) t 
~ * t (WrappedArrow a' b' c') => Rewrapped (WrappedArrow a b c) t 
~ * t (Kleisli m' a' b') => Rewrapped (Kleisli m a b) t 
~ * t (Coproduct f' g' a') => Rewrapped (Coproduct f g a) t 
~ * t (TracedT m' w' a') => Rewrapped (TracedT m w a) t 
~ * t (Compose f' g' a') => Rewrapped (Compose f g a) t 
~ * t (ComposeFC f' g' a') => Rewrapped (ComposeFC f g a) t 
~ * t (ComposeCF f' g' a') => Rewrapped (ComposeCF f g a) t 
~ * t (ContT r' m' a') => Rewrapped (ContT r m a) t 
~ * t (ErrorT e' m' a') => Rewrapped (ErrorT e m a) t 
~ * t (ReaderT r n b) => Rewrapped (ReaderT r m a) t 
~ * t (StateT s' m' a') => Rewrapped (StateT s m a) t 
~ * t (StateT s' m' a') => Rewrapped (StateT s m a) t 
~ * t (WriterT w' m' a') => Rewrapped (WriterT w m a) t 
~ * t (WriterT w' m' a') => Rewrapped (WriterT w m a) t 
~ * t (Compose f' g' a') => Rewrapped (Compose f g a) t 
~ * t (Tagged k s' a') => Rewrapped (Tagged k1 s a) t 
~ * t (RWST r' w' s' m' a') => Rewrapped (RWST r w s m a) t 
~ * t (RWST r' w' s' m' a') => Rewrapped (RWST r w s m a) t 

class (Rewrapped s t, Rewrapped t s) => Rewrapping s t Source

Instances

(Rewrapped s t, Rewrapped t s) => Rewrapping s t 

_Wrapped :: Rewrapping s t => Iso s t (Unwrapped s) (Unwrapped t)Source

Work under a newtype wrapper. 

>>> Const "hello" & _Wrapped %~ length & getConst
5

 _Wrapped   ≡ from _Unwrapped
 _Unwrapped ≡ from _Wrapped

_Unwrapped :: Rewrapping s t => Iso (Unwrapped t) (Unwrapped s) t sSource

_Wrapping :: Rewrapping s t => (Unwrapped s -> s) -> Iso s t (Unwrapped s) (Unwrapped t)Source

This is a convenient version of _Wrapped with an argument that's ignored.

The user supplied function is ignored, merely its types are used.

_Unwrapping :: Rewrapping s t => (Unwrapped s -> s) -> Iso (Unwrapped t) (Unwrapped s) t sSource

This is a convenient version of _Unwrapped with an argument that's ignored.

The user supplied function is ignored, merely its types are used.

Operations

op :: Wrapped s => (Unwrapped s -> s) -> s -> Unwrapped sSource

Given the constructor for a Wrapped type, return a deconstructor that is its inverse.

Assuming the Wrapped instance is legal, these laws hold: 

 op f . f ≡ id
 f . op f ≡ id

>>> op Identity (Identity 4)
4

>>> op Const (Const "hello")
"hello"

ala :: Rewrapping s t => (Unwrapped s -> s) -> ((Unwrapped t -> t) -> e -> s) -> e -> Unwrapped sSource

This combinator is based on ala from Conor McBride's work on Epigram.

As with _Wrapping, the user supplied function for the newtype is ignored. 

>>> ala Sum foldMap [1,2,3,4]
10

>>> ala All foldMap [True,True]
True

>>> ala All foldMap [True,False]
False

>>> ala Any foldMap [False,False]
False

>>> ala Any foldMap [True,False]
True

>>> ala Sum foldMap [1,2,3,4]
10

>>> ala Product foldMap [1,2,3,4]
24

alaf :: (Profunctor p, Rewrapping s t) => (Unwrapped s -> s) -> (p r t -> e -> s) -> p r (Unwrapped t) -> e -> Unwrapped sSource

This combinator is based on ala' from Conor McBride's work on Epigram.

As with _Wrapping, the user supplied function for the newtype is ignored. 

>>> alaf Sum foldMap length ["hello","world"]
10