{-# LANGUAGE CPP , MultiParamTypeClasses , FunctionalDependencies , FlexibleInstances , FlexibleContexts , RankNTypes , ScopedTypeVariables #-} module Lens.Micro ( (&), -- * Setting (applying a function to values) ASetter, sets, (%~), over, (.~), set, mapped, -- * Getting (retrieving a value) -- $getters-note Getting, (^.), -- * Folds (getters which return multiple elements) (^..), toListOf, (^?), (^?!), folded, has, -- * Lenses (things which are both setters and getters) Lens, Lens', lens, -- * Traversals (lenses which have multiple targets) Traversal, Traversal', both, -- * Prisms -- $prisms-note _Left, _Right, _Just, _Nothing, -- * Tuples Field1(..), Field2(..), Field3(..), Field4(..), Field5(..), ) where import Control.Applicative import Data.Functor.Identity import Data.Foldable import Data.Monoid #if __GLASGOW_HASKELL__ >= 710 import Data.Function ((&)) #endif {- $setup -- >>> import Data.Char (toUpper) -- >>> import Control.Arrow (first, second, left, right) -} #if __GLASGOW_HASKELL__ < 710 {- | '&' is a reverse application operator. This provides notational convenience. Its precedence is one higher than that of the forward application operator '$', which allows '&' to be nested in '$'. -} (&) :: a -> (a -> b) -> b a & f = f a {-# INLINE (&) #-} infixl 1 & #endif -- Setting ----------------------------------------------------------------- {- | @ASetter s t a b@ is something that turns a function modifying a value into a function modifying a /structure/. If you ignore 'Control.Monad.Identity.Identity' (as @Identity a@ is the same thing as @a@), the type is: @ type ASetter s t a b = (a -> b) -> s -> t @ This means that examples of setters you might've already seen are: * @'map' :: (a -> b) -> [a] -> [b]@ (which corresponds to 'mapped') * @'fmap' :: 'Functor' f => (a -> b) -> f a -> f b@ (which corresponds to 'mapped' as well) * @'Control.Arrow.first' :: (a -> b) -> (a, x) -> (b, x)@ (which corresponds to '_1') * @'Control.Arrow.left' :: (a -> b) -> Either a x -> Either b x@ (which corresponds to '_Left') The reason 'Control.Monad.Identity.Identity' is used here is for 'ASetter' to be composable with other types, such as 'Lens'. Technically, if you're writing a library, you shouldn't use this type for setters you are exporting from your library; the right type to use is @Setter@, but it is not provided by microlens. It's completely alright, however, to export functions which take an 'ASetter' as an argument. -} type ASetter s t a b = (a -> Identity b) -> s -> Identity t {- | 'sets' creates an 'ASetter' from an ordinary function. (The only thing it does is wrapping and unwrapping 'Control.Monad.Identity.Identity'.) -} sets :: ((a -> b) -> s -> t) -> ASetter s t a b sets f g = Identity . f (runIdentity . g) {-# INLINE sets #-} {- | ('%~') applies a function to the target; an alternative explanation is that it is an inverse of 'sets', which turns a setter into an ordinary function. @'mapped' '%~' reverse@ is the same thing as @'fmap' reverse@. See 'over' if you want a non-operator synonym. Negating the 1st element of a pair: >>> (1,2) & _1 %~ negate (-1,2) Turning all @Left@s in a list to upper case: >>> (mapped._Left.mapped %~ toUpper) [Left "foo", Right "bar"] [Left "FOO",Right "bar"] -} (%~) :: ASetter s t a b -> (a -> b) -> s -> t (%~) = over {-# INLINE (%~) #-} infixr 4 %~ {- | 'over' is a synonym for ('%~'). Getting 'fmap' in a roundabout way: @ 'over' 'mapped' :: 'Functor' f => (a -> b) -> f a -> f b 'over' 'mapped' = 'fmap' @ Applying a function to both components of a pair: @ 'over' 'both' :: (a -> b) -> (a, a) -> (b, b) 'over' 'both' = \\f t -> (f (fst t), f (snd t)) @ Using @'over' '_2'@ as a replacement for 'Control.Arrow.second': >>> over _2 show (10,20) (10,"20") -} over :: ASetter s t a b -> (a -> b) -> s -> t over l f = runIdentity . l (Identity . f) {-# INLINE over #-} {- | ('.~') assigns a value to the target. These are equivalent: @ l '.~' x l '%~' 'const' x @ See 'set' if you want a non-operator synonym. Here it is used to change 2 fields of a 3-tuple: >>> (0,0,0) & _1 .~ 1 & _3 .~ 3 (1,0,3) -} (.~) :: ASetter s t a b -> b -> s -> t (.~) = set {-# INLINE (.~) #-} infixr 4 .~ {- | 'set' is a synonym for ('.~'). Setting the 1st component of a pair: @ 'set' '_1' :: x -> (a, b) -> (x, b) 'set' '_1' = \\x t -> (x, snd t) @ Using it to rewrite ('Data.Functor.<$'): @ 'set' 'mapped' :: 'Functor' f => a -> f b -> f a 'set' 'mapped' = ('Data.Functor.<$') @ -} set :: ASetter s t a b -> b -> s -> t set l b = runIdentity . l (\_ -> Identity b) {-# INLINE set #-} {- | 'mapped' is a setter for everything contained in a functor. You can use it to map over lists, @Maybe@, or even @IO@ (which is something you can't do with 'traversed' or 'each'). Here 'mapped' is used to turn a value to all non-'Nothing' values in a list: >>> [Just 3,Nothing,Just 5] & mapped.mapped .~ 0 [Just 0,Nothing,Just 0] Keep in mind that while 'mapped' is a more powerful setter than 'each', it can't be used as a getter! This won't work (and will fail with a type error): @ [(1,2),(3,4),(5,6)] '^..' 'mapped' . 'both' @ -} mapped :: Functor f => ASetter (f a) (f b) a b mapped = sets fmap {-# INLINE mapped #-} -- Getting ----------------------------------------------------------------- {- $getters-note Getters are a not-entirely-obvious way to use (supposedly) /value-changing/ traversals to /carry out/ information from a structure. For details, see the documentation for 'Getting'. Exporting @Getter@ is impossible, as then microlens would have to depend on contravariant. -} {- | @Getting r s a@ is, in a way, equivalent to @s -> a@. Since @'Const' r a@ is the same as @r@, 'Getting' is actually @(a -> r) -> s -> r@, which is just CPS-transformed @s -> a@. The reason 'Const' and CPS are used is that we want getters to have the same shape as lenses (which we achieve because 'Const' is a functor). -} type Getting r s a = (a -> Const r a) -> s -> Const r s {- | ('^.') applies a getter to a value; in other words, it gets a value out of a structure using a getter (which can be a lens, traversal, fold, etc.). Getting 1st field of a tuple: @ ('^.' '_1') :: (a, b) -> a ('^.' '_1') = 'fst' @ When ('^.') is used with a traversal, it combines all results using the 'Monoid' instance for the resulting type. For instance, for lists it would be simple concatenation: >>> ("str","ing") ^. each "string" The reason for this is that traversals use 'Applicative', and the 'Applicative' instance for 'Const' uses monoid concatenation to combine “effects” of 'Const'. -} (^.) :: s -> Getting a s a -> a s ^. l = getConst (l Const s) {-# INLINE (^.) #-} infixl 8 ^. -- Folds ------------------------------------------------------------------- -- | A 'Monoid' for a 'Contravariant' 'Applicative'. newtype Folding f a = Folding { getFolding :: f a } instance (Applicative (Const r)) => Monoid (Folding (Const r) a) where mempty = Folding (Const . getConst $ pure ()) {-# INLINE mempty #-} Folding fr `mappend` Folding fs = Folding (fr *> fs) {-# INLINE mappend #-} {- | @s ^.. t@ returns the list of all values that @t@ gets from @s@. A 'Maybe' contains either 0 or 1 values: >>> Just 3 ^.. _Just [3] Gathering all values in a list of tuples: >>> [(1,2),(3,4)] ^.. each.each [1,2,3,4] -} (^..) :: s -> Getting (Endo [a]) s a -> [a] s ^.. l = toListOf l s {-# INLINE (^..) #-} infixl 8 ^.. {- | 'toListOf' is a synonym for ('^..'). -} toListOf :: Getting (Endo [a]) s a -> s -> [a] toListOf l = foldrOf l (:) [] {-# INLINE toListOf #-} {- | @s ^? t@ returns the 1st element @t@ returns, or 'Nothing' if @t@ doesn't return anything. It's trivially implemented by passing the 'First' monoid to the getter. Safe 'head': >>> [] ^? each Nothing >>> [1..3] ^? each Just 1 Converting 'Either' to 'Maybe': >>> Left 1 ^? _Right Nothing >>> Right 1 ^? _Right Just 1 -} (^?) :: s -> Getting (First a) s a -> Maybe a s ^? l = getFirst (foldMapOf l (First . Just) s) {-# INLINE (^?) #-} infixl 8 ^? {- | ('^?!') is an unsafe variant of ('^?') – instead of using 'Nothing' to indicate that there were no elements returned, it throws an exception. -} (^?!) :: s -> Getting (Endo a) s a -> a s ^?! l = foldrOf l const (error "(^?!): empty Fold") s {-# INLINE (^?!) #-} infixl 8 ^?! foldrOf :: Getting (Endo r) s a -> (a -> r -> r) -> r -> s -> r foldrOf l f z = flip appEndo z . foldMapOf l (Endo . f) {-# INLINE foldrOf #-} foldMapOf :: Getting r s a -> (a -> r) -> s -> r foldMapOf l f = getConst . l (Const . f) {-# INLINE foldMapOf #-} {- | 'folded' is a fold for anything 'Foldable'. In a way, it's an opposite of 'mapped' – the most powerful getter, but can't be used as a setter. -} folded :: (Foldable f, Applicative (Const r)) => Getting r (f a) a folded f = Const . getConst . getFolding . foldMap (Folding . f) {-# INLINE folded #-} {- | 'has' checks whether a getter (any getter, including lenses, traversals, and folds) returns at least 1 value. Checking whether a list is non-empty: >>> has each [] False You can also use it with e.g. '_Left' (and other 0-or-1 traversals) as a replacement for 'Data.Maybe.isNothing', 'Data.Maybe.isJust' and other @isConstructorName@ functions: >>> has _Left (Left 1) True -} has :: Getting Any s a -> s -> Bool has l = getAny . foldMapOf l (\_ -> Any True) {-# INLINE has #-} -- Lenses ------------------------------------------------------------------ {- | Lenses in a nutshell: use ('^.') to get, ('.~') to set, ('%~') to modify. ('.') composes lenses (i.e. if a @B@ is a part of @A@, and a @C@ is a part of in @B@, then @b.c@ lets you operate on @C@ inside @A@). You can create lenses with 'lens', or you can write them by hand (see below). @Lens s t a b@ is the lowest common denominator of a setter and a getter, something that has the power of both; it has a 'Functor' constraint, and since both 'Const' and 'Control.Monad.Identity.Identity' are functors, it can be used whenever a getter or a setter is needed. * @a@ is the type of the value inside of structure * @b@ is the type of the replaced value * @s@ is the type of the whole structure * @t@ is the type of the structure after replacing @a@ in it with @b@ A 'Lens' can only point at a single value inside a structure (unlike a 'Traversal'). It is easy to write lenses manually. The generic template is: @ somelens :: Lens s t a b -- “f” is the “a -> f b” function, “s” is the structure. somelens f s = let a = ... -- Extract the value from “s”. rebuildWith b = ... -- Write a function which would -- combine “s” and modified value -- to produce new structure. in rebuildWith '<$>' f a -- Apply the structure-producing -- function to the modified value. @ Here's the '_1' lens: @ _1 :: Lens (a, x) (b, x) a b _1 f (a, x) = (\\b -> (b, x)) '<$>' f a @ Here's a more complicated lens, which extracts /several/ values from a structure (in a tuple): @ type Age = Int type City = String type Country = String data Person = Person Age City Country -- This lens lets you access all location-related information about a person. location :: 'Lens'' Person (City, Country) location f (Person age city country) = (\\(city', country') -> Person age city' country') '<$>' f (city, country) @ You even can choose to use a lens to present /all/ information contained in the structure (in a different way). Such lenses are called @Iso@ in lens's terminology. For instance (assuming you don't mind functions that can error out), here's a lens which lets you act on the string representation of a value: @ string :: (Read a, Show a) => 'Lens'' a String string f s = read '<$>' f (show s) @ Using it to reverse a number: @ >>> 123 '&' string '%~' reverse 321 @ -} type Lens s t a b = forall f. Functor f => (a -> f b) -> s -> f t {- | This is a type alias for monomorphic lenses which don't change the type of the container (or of the value inside). -} type Lens' s a = Lens s s a a {- | 'lens' creates a 'Lens' from a getter and a setter. The resulting lens isn't the most effective one (because of having to traverse the structure twice when modifying), but it shouldn't matter much. A (partial) lens for list indexing: @ ix :: Int -> 'Lens'' [a] a ix i = 'lens' ('!!' i) -- getter (\\s b -> take i s ++ b : drop (i+1) s) -- setter @ Usage: @ >>> [1..9] '^.' ix 3 4 >>> [1..9] & ix 3 '%~' negate [1,2,3,-4,5,6,7,8,9] @ When getting, the setter is completely unused. When setting, the getter is unused. Both are used only when the value is being modified. Here's an example of using a lens targeting the head of a list. The getter is replaced with 'undefined' to make sure it's not used: >>> [1,2,3] & lens undefined (\s b -> b : tail s) .~ 10 [10,2,3] -} lens :: (s -> a) -> (s -> b -> t) -> Lens s t a b lens sa sbt afb s = sbt s <$> afb (sa s) {-# INLINE lens #-} -- Traversals -------------------------------------------------------------- {- | Traversals in a nutshell: they're like lenses but they can point at multiple values. Use ('^..') (not '^.') to get all values, ('^?') to get the 1st value, ('.~') to set values, ('%~') to modify them. ('.') composes traversals just as it composes lenses. @Traversal s t a b@ is a generalisation of 'Lens' which allows many targets (possibly 0). It's achieved by changing the constraint to 'Applicative' instead of 'Functor' – indeed, the point of 'Applicative' is that you can combine effects, which is just what we need to have many targets. Traversals don't differ from lenses when it comes to setting – you can use usual ('%~') and ('.~') to modify and set values. Getting is a bit different, because you have to decide what to do in the case of multiple values. In particular, you can use these combinators (as well as everything else in the “Folds” section): * ('^..') gets a list of values * ('^?') gets the 1st value (or 'Nothing' if there are no values) * ('^?!') gets the 1st value and throws an exception if there are no values In addition, ('^.') works for traversals as well – it combines traversed values using the ('<>') operation (if the values are instances of 'Monoid'). Traversing any value twice is a violation of traversal laws. You can, however, traverse values in any order. Ultimately, traversals should follow 2 laws: @ t pure ≡ pure fmap (t f) . t g ≡ getCompose . t (Compose . fmap f . g) @ The 1st law states that you can't change the shape of the structure or do anything funny with elements (traverse elements which aren't in the structure, create new elements out of thin air, etc.). The 2nd law states that you should be able to fuse 2 identical traversals into one. For a more detailed explanation of the laws, see <http://artyom.me/lens-over-tea-2#traversal-laws this blog post> (if you prefer rambling blog posts), or <https://www.cs.ox.ac.uk/jeremy.gibbons/publications/iterator.pdf The Essence Of The Iterator Pattern> (if you prefer papers). -} type Traversal s t a b = forall f. Applicative f => (a -> f b) -> s -> f t {- | This is a type alias for monomorphic traversals which don't change the type of the container (or of the values inside). -} type Traversal' s a = Traversal s s a a {- | 'both' traverses both fields of a tuple. Unlike @both@ from lens, it only works for pairs – not for triples or 'Either'. >>> ("str","ing") ^. both "string" >>> ("str","ing") & both %~ reverse ("rts","gni") -} both :: Traversal (a, a) (b, b) a b both f = \ ~(a, b) -> liftA2 (,) (f a) (f b) {-# INLINE both #-} -- Prisms ------------------------------------------------------------------ {- $prisms-note Prisms are traversals which always target 0 or 1 values. Moreover, it's possible to /reverse/ a prism, using it to construct a structure instead of peeking into it. Here's an example from the lens library: @ >>> over _Left (+1) (Left 2) Left 3 >>> _Left # 5 Left 5 @ However, it's not possible for microlens to export prisms, because their type depends on @Choice@, which resides in the profunctors library, which is a somewhat huge dependency. So, all prisms included here are traversals instead. -} {- | '_Left' targets the value contained in an 'Either', provided it's a 'Left'. Gathering all @Left@s in a structure (like the 'Data.Either.lefts' function): @ 'toListOf' ('each' . '_Left') :: ['Either' a b] -> [a] 'toListOf' ('each' . '_Left') = 'Data.Either.lefts' @ Checking whether an 'Either' is a 'Left' (like 'Data.Either.isLeft'): >>> has _Left (Left 1) True >>> has _Left (Right 1) False Extracting a value (if you're sure it's a 'Left'): >>> Left 1 ^?! _Left 1 Mapping over all @Left@s: >>> (each._Left %~ map toUpper) [Left "foo", Right "bar"] [Left "FOO",Right "bar"] Implementation: @ '_Left' f (Left a) = 'Left' '<$>' f a '_Left' _ (Right b) = 'pure' ('Right' b) @ -} _Left :: Traversal (Either a b) (Either a' b) a a' _Left f (Left a) = Left <$> f a _Left _ (Right b) = pure (Right b) {-# INLINE _Left #-} {- | '_Right' targets the value contained in an 'Either', provided it's a 'Right'. See documentation for '_Left'. -} _Right :: Traversal (Either a b) (Either a b') b b' _Right f (Right b) = Right <$> f b _Right _ (Left a) = pure (Left a) {-# INLINE _Right #-} {- | '_Just' targets the value contained in a 'Maybe', provided it's a 'Just'. See documentation for '_Left' (as these 2 are pretty similar). In particular, it can be used to write these: * Unsafely extracting a value from a 'Just': @ 'Data.Maybe.fromJust' = ('^?!' '_Just') @ * Checking whether a value is a 'Just': @ 'Data.Maybe.isJust' = 'has' '_Just' @ * Converting a 'Maybe' to a list (empty or consisting of a single element): @ 'Data.Maybe.maybeToList' = ('^..' '_Just') @ * Gathering all @Just@s in a list: @ 'Data.Maybe.catMaybes' = ('^..' 'each' . '_Just') @ -} _Just :: Traversal (Maybe a) (Maybe a') a a' _Just f (Just a) = Just <$> f a _Just _ Nothing = pure Nothing {-# INLINE _Just #-} {- | '_Nothing' targets a @()@ if the 'Maybe' is a 'Nothing', and doesn't target anything otherwise: >>> Just 1 ^.. _Nothing [] >>> Nothing ^.. _Nothing [()] It's not particularly useful (unless you want to use @'has' '_Nothing'@ as a replacement for 'Data.Maybe.isNothing'), and provided mainly for consistency. Implementation: @ '_Nothing' f Nothing = 'const' 'Nothing' '<$>' f () '_Nothing' _ j = 'pure' j @ -} _Nothing :: Traversal' (Maybe a) () _Nothing f Nothing = const Nothing <$> f () _Nothing _ j = pure j {-# INLINE _Nothing #-} -- Tuples ------------------------------------------------------------------ -- Commented instances amount to ~0.8s of building time. class Field1 s t a b | s -> a, t -> b, s b -> t, t a -> s where {- | Gives access to the 1st field of a tuple (up to 5-tuples). Getting the 1st component: >>> (1,2,3,4,5) ^. _1 1 Setting the 1st component: >>> (1,2,3) & _1 .~ 10 (10,2,3) Note that this lens is lazy, and can set fields even of 'undefined': >>> set _1 10 undefined :: (Int, Int) (10,*** Exception: Prelude.undefined This is done to avoid violating a lens law stating that you can get back what you put: >>> view _1 . set _1 10 $ (undefined :: (Int, Int)) 10 The implementation (for 2-tuples) is: @ '_1' f t = (,) '<$>' f (fst t) '<*>' 'pure' (snd t) @ or, alternatively, @ '_1' f ~(a,b) = (\\a' -> (a',b)) '<$>' f a @ (where @~@ means a lazy pattern). -} _1 :: Lens s t a b instance Field1 (a,b) (a',b) a a' where _1 k ~(a,b) = (\a' -> (a',b)) <$> k a {-# INLINE _1 #-} instance Field1 (a,b,c) (a',b,c) a a' where _1 k ~(a,b,c) = (\a' -> (a',b,c)) <$> k a {-# INLINE _1 #-} instance Field1 (a,b,c,d) (a',b,c,d) a a' where _1 k ~(a,b,c,d) = (\a' -> (a',b,c,d)) <$> k a {-# INLINE _1 #-} instance Field1 (a,b,c,d,e) (a',b,c,d,e) a a' where _1 k ~(a,b,c,d,e) = (\a' -> (a',b,c,d,e)) <$> k a {-# INLINE _1 #-} {- instance Field1 (a,b,c,d,e,f) (a',b,c,d,e,f) a a' where _1 k ~(a,b,c,d,e,f) = (\a' -> (a',b,c,d,e,f)) <$> k a {-# INLINE _1 #-} instance Field1 (a,b,c,d,e,f,g) (a',b,c,d,e,f,g) a a' where _1 k ~(a,b,c,d,e,f,g) = (\a' -> (a',b,c,d,e,f,g)) <$> k a {-# INLINE _1 #-} instance Field1 (a,b,c,d,e,f,g,h) (a',b,c,d,e,f,g,h) a a' where _1 k ~(a,b,c,d,e,f,g,h) = (\a' -> (a',b,c,d,e,f,g,h)) <$> k a {-# INLINE _1 #-} instance Field1 (a,b,c,d,e,f,g,h,i) (a',b,c,d,e,f,g,h,i) a a' where _1 k ~(a,b,c,d,e,f,g,h,i) = (\a' -> (a',b,c,d,e,f,g,h,i)) <$> k a {-# INLINE _1 #-} -} class Field2 s t a b | s -> a, t -> b, s b -> t, t a -> s where {- | Gives access to the 2nd field of a tuple (up to 5-tuples). See documentation for '_1'. -} _2 :: Lens s t a b instance Field2 (a,b) (a,b') b b' where _2 k ~(a,b) = (\b' -> (a,b')) <$> k b {-# INLINE _2 #-} instance Field2 (a,b,c) (a,b',c) b b' where _2 k ~(a,b,c) = (\b' -> (a,b',c)) <$> k b {-# INLINE _2 #-} instance Field2 (a,b,c,d) (a,b',c,d) b b' where _2 k ~(a,b,c,d) = (\b' -> (a,b',c,d)) <$> k b {-# INLINE _2 #-} instance Field2 (a,b,c,d,e) (a,b',c,d,e) b b' where _2 k ~(a,b,c,d,e) = (\b' -> (a,b',c,d,e)) <$> k b {-# INLINE _2 #-} {- instance Field2 (a,b,c,d,e,f) (a,b',c,d,e,f) b b' where _2 k ~(a,b,c,d,e,f) = (\b' -> (a,b',c,d,e,f)) <$> k b {-# INLINE _2 #-} instance Field2 (a,b,c,d,e,f,g) (a,b',c,d,e,f,g) b b' where _2 k ~(a,b,c,d,e,f,g) = (\b' -> (a,b',c,d,e,f,g)) <$> k b {-# INLINE _2 #-} instance Field2 (a,b,c,d,e,f,g,h) (a,b',c,d,e,f,g,h) b b' where _2 k ~(a,b,c,d,e,f,g,h) = (\b' -> (a,b',c,d,e,f,g,h)) <$> k b {-# INLINE _2 #-} instance Field2 (a,b,c,d,e,f,g,h,i) (a,b',c,d,e,f,g,h,i) b b' where _2 k ~(a,b,c,d,e,f,g,h,i) = (\b' -> (a,b',c,d,e,f,g,h,i)) <$> k b {-# INLINE _2 #-} -} class Field3 s t a b | s -> a, t -> b, s b -> t, t a -> s where {- | Gives access to the 3rd field of a tuple (up to 5-tuples). See documentation for '_1'. -} _3 :: Lens s t a b instance Field3 (a,b,c) (a,b,c') c c' where _3 k ~(a,b,c) = (\c' -> (a,b,c')) <$> k c {-# INLINE _3 #-} instance Field3 (a,b,c,d) (a,b,c',d) c c' where _3 k ~(a,b,c,d) = (\c' -> (a,b,c',d)) <$> k c {-# INLINE _3 #-} instance Field3 (a,b,c,d,e) (a,b,c',d,e) c c' where _3 k ~(a,b,c,d,e) = (\c' -> (a,b,c',d,e)) <$> k c {-# INLINE _3 #-} {- instance Field3 (a,b,c,d,e,f) (a,b,c',d,e,f) c c' where _3 k ~(a,b,c,d,e,f) = (\c' -> (a,b,c',d,e,f)) <$> k c {-# INLINE _3 #-} instance Field3 (a,b,c,d,e,f,g) (a,b,c',d,e,f,g) c c' where _3 k ~(a,b,c,d,e,f,g) = (\c' -> (a,b,c',d,e,f,g)) <$> k c {-# INLINE _3 #-} instance Field3 (a,b,c,d,e,f,g,h) (a,b,c',d,e,f,g,h) c c' where _3 k ~(a,b,c,d,e,f,g,h) = (\c' -> (a,b,c',d,e,f,g,h)) <$> k c {-# INLINE _3 #-} instance Field3 (a,b,c,d,e,f,g,h,i) (a,b,c',d,e,f,g,h,i) c c' where _3 k ~(a,b,c,d,e,f,g,h,i) = (\c' -> (a,b,c',d,e,f,g,h,i)) <$> k c {-# INLINE _3 #-} -} class Field4 s t a b | s -> a, t -> b, s b -> t, t a -> s where {- | Gives access to the 4th field of a tuple (up to 5-tuples). See documentation for '_1'. -} _4 :: Lens s t a b instance Field4 (a,b,c,d) (a,b,c,d') d d' where _4 k ~(a,b,c,d) = (\d' -> (a,b,c,d')) <$> k d {-# INLINE _4 #-} instance Field4 (a,b,c,d,e) (a,b,c,d',e) d d' where _4 k ~(a,b,c,d,e) = (\d' -> (a,b,c,d',e)) <$> k d {-# INLINE _4 #-} {- instance Field4 (a,b,c,d,e,f) (a,b,c,d',e,f) d d' where _4 k ~(a,b,c,d,e,f) = (\d' -> (a,b,c,d',e,f)) <$> k d {-# INLINE _4 #-} instance Field4 (a,b,c,d,e,f,g) (a,b,c,d',e,f,g) d d' where _4 k ~(a,b,c,d,e,f,g) = (\d' -> (a,b,c,d',e,f,g)) <$> k d {-# INLINE _4 #-} instance Field4 (a,b,c,d,e,f,g,h) (a,b,c,d',e,f,g,h) d d' where _4 k ~(a,b,c,d,e,f,g,h) = (\d' -> (a,b,c,d',e,f,g,h)) <$> k d {-# INLINE _4 #-} instance Field4 (a,b,c,d,e,f,g,h,i) (a,b,c,d',e,f,g,h,i) d d' where _4 k ~(a,b,c,d,e,f,g,h,i) = (\d' -> (a,b,c,d',e,f,g,h,i)) <$> k d {-# INLINE _4 #-} -} class Field5 s t a b | s -> a, t -> b, s b -> t, t a -> s where {- | Gives access to the 5th field of a tuple (only for 5-tuples). See documentation for '_1'. -} _5 :: Lens s t a b instance Field5 (a,b,c,d,e) (a,b,c,d,e') e e' where _5 k ~(a,b,c,d,e) = (\e' -> (a,b,c,d,e')) <$> k e {-# INLINE _5 #-} {- instance Field5 (a,b,c,d,e,f) (a,b,c,d,e',f) e e' where _5 k ~(a,b,c,d,e,f) = (\e' -> (a,b,c,d,e',f)) <$> k e {-# INLINE _5 #-} instance Field5 (a,b,c,d,e,f,g) (a,b,c,d,e',f,g) e e' where _5 k ~(a,b,c,d,e,f,g) = (\e' -> (a,b,c,d,e',f,g)) <$> k e {-# INLINE _5 #-} instance Field5 (a,b,c,d,e,f,g,h) (a,b,c,d,e',f,g,h) e e' where _5 k ~(a,b,c,d,e,f,g,h) = (\e' -> (a,b,c,d,e',f,g,h)) <$> k e {-# INLINE _5 #-} instance Field5 (a,b,c,d,e,f,g,h,i) (a,b,c,d,e',f,g,h,i) e e' where _5 k ~(a,b,c,d,e,f,g,h,i) = (\e' -> (a,b,c,d,e',f,g,h,i)) <$> k e {-# INLINE _5 #-} -}