Implement indexed optics

src/Control/Lens.idr

@@ -4,6 +4,7 @@ import public Control.Lens.At
 import public Control.Lens.Equality
 import public Control.Lens.Fold
 import public Control.Lens.Getter
+import public Control.Lens.Indexed
 import public Control.Lens.Iso
 import public Control.Lens.Lens
 import public Control.Lens.Optic

src/Control/Lens/Fold.idr

@@ -6,6 +6,7 @@ import Data.Profunctor.Costrong
 import Data.Profunctor.Traversing
 import Control.Applicative.Backwards
 import Control.Lens.Optic
+import Control.Lens.Indexed
 import Control.Lens.OptionalFold
 import Control.Lens.Traversal
 
@@ -39,7 +40,11 @@ foldToTraversal @{MkIsFold _} = MkIsTraversal %search
 ||| `Fold s a` is equivalent to `s -> List a`.
 public export
 0 Fold : (s,a : Type) -> Type
-Fold s a = Optic IsFold s s a a
+Fold = Simple (Optic IsFold)
+
+public export
+0 IndexedFold : (i,s,a : Type) -> Type
+IndexedFold = Simple . IndexedOptic IsFold
 
 
 ------------------------------------------------------------------------------
@@ -68,6 +73,12 @@ public export
 folding : Foldable f => (s -> f a) -> Fold s a
 folding @{_} f @{MkIsFold _} = rphantom . contramapFst f . wander traverse_
 
+public export
+ifolding : Foldable f => (s -> f (i, a)) -> IndexedFold i s a
+ifolding @{_} f @{MkIsFold _} @{ind} =
+  rphantom . contramapFst f . wander traverse_  . indexed @{ind}
+
+
 ||| Reverse the order of a fold's focuses.
 public export
 backwards : Fold s a -> Fold s a
@@ -98,18 +109,30 @@ public export
 foldMapOf : Monoid m => Fold s a -> (a -> m) -> s -> m
 foldMapOf l = runForget . l . MkForget
 
+public export
+ifoldMapOf : Monoid m => IndexedFold i s a -> (i -> a -> m) -> s -> m
+ifoldMapOf l = runForget . l @{%search} @{Idxed} . MkForget . uncurry
+
 ||| Combine the focuses of an optic using the provided function, starting from
 ||| the right.
 public export
 foldrOf : Fold s a -> (a -> acc -> acc) -> acc -> s -> acc
 foldrOf l = flip . foldMapOf @{MkMonoid @{MkSemigroup (.)} id} l
 
+public export
+ifoldrOf : IndexedFold i s a -> (i -> a -> acc -> acc) -> acc -> s -> acc
+ifoldrOf l = flip . ifoldMapOf @{MkMonoid @{MkSemigroup (.)} id} l
+
 ||| Combine the focuses of an optic using the provided function, starting from
 ||| the left.
 public export
 foldlOf : Fold s a -> (acc -> a -> acc) -> acc -> s -> acc
 foldlOf l = flip . foldMapOf @{MkMonoid @{MkSemigroup $ flip (.)} id} l . flip
 
+public export
+ifoldlOf : IndexedFold i s a -> (i -> acc -> a -> acc) -> acc -> s -> acc
+ifoldlOf l = flip . ifoldMapOf @{MkMonoid @{MkSemigroup $ flip (.)} id} l . (flip .)
+
 ||| Combine each focus value of an optic using a monoid structure.
 public export
 concatOf : Monoid m => Fold s m -> s -> m
@@ -135,11 +158,21 @@ traverseOf_ l f =
   let _ = MkMonoid @{MkSemigroup (*>)} (pure ())
   in foldMapOf l (ignore . f)
 
+public export
+itraverseOf_ : Applicative f => IndexedFold i s a -> (i -> a -> f b) -> s -> f ()
+itraverseOf_ l f =
+  let _ = MkMonoid @{MkSemigroup (*>)} (pure ())
+  in ifoldMapOf l (ignore .: f)
+
 ||| A version of `traverseOf_` with the arguments flipped.
 public export
 forOf_ : Applicative f => Fold s a -> s -> (a -> f b) -> f ()
 forOf_ = flip . traverseOf_
 
+public export
+iforOf_ : Applicative f => IndexedFold i s a -> s -> (i -> a -> f b) -> f ()
+iforOf_ = flip . itraverseOf_
+
 ||| The conjunction of an optic containing lazy boolean values.
 public export
 andOf : Fold s (Lazy Bool) -> s -> Bool
@@ -179,12 +212,22 @@ public export
 firstOf : Fold s a -> s -> Maybe a
 firstOf l = foldMapOf l Just
 
+public export
+ifirstOf : IndexedFold i s a -> s -> Maybe (i, a)
+ifirstOf l = runForget $ l @{%search} @{Idxed} $ MkForget Just
+
 ||| Access the last focus value of an optic, returning `Nothing` if there are
 ||| no focuses.
 public export
 lastOf : Fold s a -> s -> Maybe a
 lastOf l = foldMapOf @{MkMonoid @{MkSemigroup $ flip (<+>)} neutral} l Just
 
+public export
+ilastOf : IndexedFold i s a -> s -> Maybe (i, a)
+ilastOf l =
+  let _ = MkMonoid @{MkSemigroup $ flip (<+>)} neutral
+  in runForget $ l @{%search} @{Idxed} $ MkForget Just
+
 
 
 ------------------------------------------------------------------------------
@@ -225,7 +268,18 @@ infixl 8 ^?
 ||| This is the operator form of `preview`.
 public export
 (^?) : s -> Fold s a -> Maybe a
-(^?) s l = preview l s
+(^?) x l = preview l x
+
+
+public export
+ipreview : IndexedFold i s a -> s -> Maybe (i, a)
+ipreview = ifirstOf
+
+infixl 8 ^@?
+
+public export
+(^@?) : s -> IndexedFold i s a -> Maybe (i, a)
+(^@?) x l = ipreview l x
 
 
 ||| Convert a `Fold` into an `OptionalFold` that accesses the first focus element.
@@ -235,6 +289,10 @@ public export
 pre : Fold s a -> OptionalFold s a
 pre = folding . preview
 
+public export
+ipre : IndexedFold i s a -> IndexedOptionalFold i s a
+ipre = ifolding . ipreview
+
 
 ||| Return a list of all focuses of a fold.
 public export
@@ -249,3 +307,14 @@ infixl 8 ^..
 public export
 (^..) : s -> Fold s a -> List a
 (^..) s l = toListOf l s
+
+
+public export
+itoListOf : IndexedFold i s a -> s -> List (i, a)
+itoListOf l = ifoldrOf l ((::) .: (,)) []
+
+infixl 8 ^@..
+
+public export
+(^@..) : s -> IndexedFold i s a -> List (i, a)
+(^@..) x l = itoListOf l x

src/Control/Lens/Getter.idr

@@ -4,6 +4,7 @@ import Data.Bicontravariant
 import Data.Profunctor
 import Data.Profunctor.Costrong
 import Control.Lens.Optic
+import Control.Lens.Indexed
 import Control.Lens.Lens
 
 %default total
@@ -31,6 +32,10 @@ public export
 0 Getter : (s,a : Type) -> Type
 Getter = Simple (Optic IsGetter)
 
+public export
+0 IndexedGetter : (i,s,a : Type) -> Type
+IndexedGetter = Simple . IndexedOptic IsGetter
+
 
 ------------------------------------------------------------------------------
 -- Utilities for getters
@@ -42,6 +47,10 @@ public export
 to : (s -> a) -> Getter s a
 to f @{MkIsGetter _} = lmap f . rphantom
 
+public export
+ito : (s -> (i, a)) -> IndexedGetter i s a
+ito f @{MkIsGetter _} @{ind} = lmap f . rphantom . indexed @{ind}
+
 ||| Construct a getter that always returns a constant value.
 public export
 like : a -> Getter s a
@@ -50,7 +59,7 @@ like = to . const
 
 ||| Access the value of an optic and apply a function to it, returning the result.
 public export
-views : Getter s a -> (a -> r) -> (s -> r)
+views : Getter s a -> (a -> r) -> s -> r
 views l = runForget . l . MkForget
 
 ||| Access the focus value of an optic, particularly a `Getter`.
@@ -58,8 +67,17 @@ public export
 view : Getter s a -> s -> a
 view l = views l id
 
+public export
+iviews : IndexedGetter i s a -> (i -> a -> r) -> s -> r
+iviews l = runForget . l @{%search} @{Idxed} . MkForget . uncurry
+
+public export
+iview : IndexedGetter i s a -> s -> (i, a)
+iview l = runForget $ l @{%search} @{Idxed} $ MkForget id
+
 
 infixl 8 ^.
+infixl 8 ^@.
 
 ||| Access the focus value of an optic, particularly a `Getter`.
 |||
@@ -67,3 +85,7 @@ infixl 8 ^.
 public export
 (^.) : s -> Getter s a -> a
 (^.) x l = view l x
+
+public export
+(^@.) : s -> IndexedGetter i s a -> (i, a)
+(^@.) x l = iview l x

src/Control/Lens/Indexed.idr

@@ -0,0 +1,33 @@
+module Control.Lens.Indexed
+
+import Data.Profunctor
+import Control.Lens.Optic
+import Control.Lens.Iso
+
+%default total
+
+
+public export
+interface Indexable i (0 p, p' : Type -> Type -> Type) | p, p' where
+  indexed : p' a b -> p (i, a) b
+
+
+-- Non-indexed use (default)
+public export
+IsIso p => Indexable i p p where
+  indexed @{MkIsIso _} = lmap snd
+
+-- Indexed use
+public export
+[Idxed] Indexable i p (p . (i,)) where
+  indexed = id
+
+
+public export
+0 IndexedOptic' : (Type -> Type -> Type) -> (i,s,t,a,b : Type) -> Type
+IndexedOptic' p i s t a b = forall p'. Indexable i p p' => p' a b -> p s t
+
+public export
+0 IndexedOptic : ((Type -> Type -> Type) -> Type) -> (i,s,t,a,b : Type) -> Type
+IndexedOptic constr i s t a b =
+  forall p,p'. constr p => Indexable i p p' => p' a b -> p s t

src/Control/Lens/Lens.idr

@@ -4,6 +4,7 @@ import Data.Profunctor
 import Data.Profunctor.Yoneda
 import Control.Monad.State
 import Control.Lens.Optic
+import Control.Lens.Indexed
 import Control.Lens.Equality
 import Control.Lens.Iso
 
@@ -48,6 +49,14 @@ public export
 0 Lens' : (s,a : Type) -> Type
 Lens' = Simple Lens
 
+public export
+0 IndexedLens : (i,s,t,a,b : Type) -> Type
+IndexedLens = IndexedOptic IsLens
+
+public export
+0 IndexedLens' : (i,s,a : Type) -> Type
+IndexedLens' = Simple . IndexedLens
+
 
 ------------------------------------------------------------------------------
 -- Utilities for lenses
@@ -63,6 +72,16 @@ public export
 lens : (get : s -> a) -> (set : s -> b -> t) -> Lens s t a b
 lens get set @{MkIsLens _} = dimap (\x => (x, get x)) (uncurry set) . second
 
+public export
+ilens : (get : s -> (i, a)) -> (set : s -> b -> t) -> IndexedLens i s t a b
+ilens get set @{_} @{ind} = lens get set . indexed @{ind}
+
+
+public export
+withIndex : i -> Lens s t a b -> IndexedLens i s t a b
+withIndex i l @{MkIsLens _} @{ind} = l . lmap (i,) . indexed @{ind}
+
+
 ||| Extract getter and setter functions from a lens.
 public export
 getLens : Lens s t a b -> (s -> a, s -> b -> t)
@@ -83,8 +102,8 @@ withLens l f = uncurry f (getLens l)
 
 ||| `Void` vacuously "contains" a value of any other type.
 public export
-devoid : Lens Void Void a b
+devoid : IndexedLens i Void Void a b
-devoid @{MkIsLens _} = dimap absurd snd . first
+devoid @{MkIsLens _} = ilens absurd const
 
 ||| All values contain a unit.
 public export
@@ -114,18 +133,19 @@ fusing @{MkIsIso _} l = proextract . l . propure
 -- Operators
 ------------------------------------------------------------------------------
 
-infixr 4 %%~; infix 4 %%=
+infixr 4 %%~; infix 4 %%=; infix 4 %%@~; infix 4 %%@=
 
-infixr 4 <%~; infixr 4 <+~; infixr 4 <*~; infixr 4 <-~; infixr 4 </~
+infixr 4 <%~; infixr 4 <%@~; infixr 4 <+~; infixr 4 <*~; infixr 4 <-~
-infixr 4 <||~; infixr 4 <&&~; infixr 4 <<+>~
+infixr 4 </~; infixr 4 <||~; infixr 4 <&&~; infixr 4 <<+>~
 
-infixr 4 <<%~; infixr 4 <<.~; infixr 4 <<?~; infixr 4 <<+~; infixr 4 <<*~
+infixr 4 <<%~; infixr 4 <<%@~; infixr 4 <<.~; infixr 4 <<?~; infixr 4 <<+~
-infixr 4 <<-~; infixr 4 <</~; infixr 4 <<||~; infixr 4 <<&&~; infixr 4 <<<+>~
+infixr 4 <<*~; infixr 4 <<-~; infixr 4 <</~; infixr 4 <<||~; infixr 4 <<&&~
+infixr 4 <<<+>~
 
-infix 4 <%=; infix 4 <+=; infix 4 <*=; infix 4 <-=; infix 4 </=
+infix 4 <%=; infix 4 <%@=; infix 4 <+=; infix 4 <*=; infix 4 <-=; infix 4 </=
 infix 4 <||=; infix 4 <&&=; infix 4 <<+>=
 
-infix 4 <<%=; infix 4 <<.=; infix 4 <<?=; infix 4 <<+=; infix 4 <<*=
+infix 4 <<%=; infix 4 <<%@=; infix 4 <<.=; infix 4 <<?=; infix 4 <<+=; infix 4 <<*=
 infix 4 <<-=; infix 4 <</=; infix 4 <<||=; infix 4 <<&&=; infix 4 <<<+>=
 
 infixr 2 <<~
@@ -139,12 +159,26 @@ public export
 (%%=) : MonadState s m => Lens s s a b -> (a -> (r, b)) -> m r
 (%%=) = (state . (swap .)) .: (%%~)
 
+public export
+(%%@~) : Functor f => IndexedLens i s t a b -> (i -> a -> f b) -> s -> f t
+(%%@~) l = applyStar . l {p=Star f} @{%search} @{Idxed}
+            . MkStar . uncurry
+
+public export
+(%%@=) : MonadState s m => IndexedLens i s s a b -> (i -> a -> (r, b)) -> m r
+(%%@=) = (state . (swap .)) .: (%%@~)
+
 
 ||| Modify a value with pass-through.
 public export
 (<%~) : Lens s t a b -> (a -> b) -> s -> (b, t)
 (<%~) l f = l %%~ (\x => (x,x)) . f
 
+||| Modify a value with pass-through, having access to the index.
+public export
+(<%@~) : IndexedLens i s t a b -> (i -> a -> b) -> s -> (b, t)
+(<%@~) l f = l %%@~ (\x => (x,x)) .: f
+
 ||| Add a value to the lens with pass-through.
 public export
 (<+~) : Num a => Lens s t a a -> a -> s -> (a, t)
@@ -195,6 +229,10 @@ public export
 (<<%~) : Lens s t a b -> (a -> b) -> s -> (a, t)
 (<<%~) l f = l %%~ (\x => (x, f x))
 
+||| Modify the value of an indexed lens and return the old value.
+(<<%@~) : IndexedLens i s t a b -> (i -> a -> b) -> s -> (a, t)
+(<<%@~) l f = l %%@~ (\i,x => (x, f i x))
+
 ||| Set the value of a lens and return the old value.
 public export
 (<<.~) : Lens s t a b -> b -> s -> (a, t)
@@ -256,6 +294,11 @@ public export
 (<%=) : MonadState s m => Lens s s a b -> (a -> b) -> m b
 (<%=) = (state . (swap .)) .: (<%~)
 
+||| Modify within a state monad with pass-through, having access to the index.
+public export
+(<%@=) : MonadState s m => IndexedLens i s s a b -> (i -> a -> b) -> m b
+(<%@=) = (state . (swap .)) .: (<%@~)
+
 ||| Add a value to the lens into state with pass-through.
 public export
 (<+=) : Num a => MonadState s m => Lens' s a -> a -> m a
@@ -297,6 +340,11 @@ public export
 (<<%=) : MonadState s m => Lens s s a b -> (a -> b) -> m a
 (<<%=) = (state . (swap .)) .: (<<%~)
 
+||| Modify the value of an indexed lens into state and return the old value.
+public export
+(<<%@=) : MonadState s m => IndexedLens i s s a b -> (i -> a -> b) -> m a
+(<<%@=) = (state . (swap .)) .: (<<%@~)
+
 ||| Set the value of a lens into state and return the old value.
 public export
 (<<.=) : MonadState s m => Lens s s a b -> b -> m a

src/Control/Lens/Optic.idr

@@ -1,5 +1,6 @@
 module Control.Lens.Optic
 
+import Data.Tensor
 import Data.Profunctor
 
 %default total
@@ -17,3 +18,4 @@ Optic' p s t a b = p a b -> p s t
 public export
 0 Optic : ((Type -> Type -> Type) -> Type) -> (s,t,a,b : Type) -> Type
 Optic constr s t a b = forall p. constr p => Optic' p s t a b
+

src/Control/Lens/Optional.idr

@@ -2,6 +2,7 @@ module Control.Lens.Optional
 
 import Data.Profunctor
 import Control.Lens.Optic
+import Control.Lens.Indexed
 import Control.Lens.Lens
 import Control.Lens.Prism
 
@@ -38,6 +39,14 @@ public export
 0 Optional' : (s,a : Type) -> Type
 Optional' = Simple Optional
 
+public export
+0 IndexedOptional : (i,s,t,a,b : Type) -> Type
+IndexedOptional = IndexedOptic IsOptional
+
+public export
+0 IndexedOptional' : (i,s,a : Type) -> Type
+IndexedOptional' = Simple . IndexedOptional
+
 
 ------------------------------------------------------------------------------
 -- Utilities for Optionals
@@ -61,10 +70,19 @@ public export
 optional' : (s -> Maybe a) -> (s -> b -> s) -> Optional s s a b
 optional' prj = optional (\x => maybe (Left x) Right (prj x))
 
+public export
+ioptional : (s -> Either t (i, a)) -> (s -> b -> t) -> IndexedOptional i s t a b
+ioptional prj set @{_} @{ind} = optional prj set . indexed @{ind}
+
+public export
+ioptional' : (s -> Maybe (i, a)) -> (s -> b -> s) -> IndexedOptional i s s a b
+ioptional' prj = ioptional (\x => maybe (Left x) Right (prj x))
+
+
 ||| The trivial optic that has no focuses.
 public export
-ignored : Optional s s a b
+ignored : IndexedOptional i s s a b
-ignored = optional' (const Nothing) const
+ignored = ioptional' (const Nothing) const
 
 
 ||| Extract projection and setter functions from an optional.
@@ -93,5 +111,5 @@ withOptional l f = uncurry f (getOptional l)
 ||| Retrieve the focus value of an optional, or allow its type to change if there
 ||| is no focus.
 public export
-matching : Prism s t a b -> s -> Either t a
+matching : Optional s t a b -> s -> Either t a
-matching = snd . getPrism
+matching = fst . getOptional

src/Control/Lens/OptionalFold.idr

@@ -4,6 +4,7 @@ import Data.Bicontravariant
 import Data.Profunctor
 import Data.Profunctor.Costrong
 import Control.Lens.Optic
+import Control.Lens.Indexed
 import Control.Lens.Optional
 import Control.Lens.Getter
 
@@ -35,6 +36,10 @@ public export
 0 OptionalFold : (s,a : Type) -> Type
 OptionalFold = Simple (Optic IsOptFold)
 
+public export
+0 IndexedOptionalFold : (i,s,a : Type) -> Type
+IndexedOptionalFold = Simple . IndexedOptic IsOptFold
+
 
 ------------------------------------------------------------------------------
 -- Utilities for OptionalFolds
@@ -47,6 +52,12 @@ folding : (s -> Maybe a) -> OptionalFold s a
 folding f @{MkIsOptFold _} =
   contrabimap (\x => maybe (Left x) Right (f x)) Left . right
 
+public export
+ifolding : (s -> Maybe (i, a)) -> IndexedOptionalFold i s a
+ifolding f @{MkIsOptFold _} @{ind} =
+  contrabimap (\x => maybe (Left x) Right (f x)) Left . right . indexed @{ind}
+
+
 ||| Construct an `OptionalFold` that can be used to filter the focuses
 ||| of another optic.
 |||

src/Control/Lens/Prism.idr

@@ -2,6 +2,7 @@ module Control.Lens.Prism
 
 import Data.Profunctor
 import Control.Lens.Optic
+import Control.Lens.Indexed
 import Control.Lens.Iso
 
 %default total
@@ -37,6 +38,14 @@ public export
 0 Prism' : (s,a : Type) -> Type
 Prism' = Simple Prism
 
+public export
+0 IndexedPrism : (i,s,t,a,b : Type) -> Type
+IndexedPrism = IndexedOptic IsPrism
+
+public export
+0 IndexedPrism' : (i,s,a : Type) -> Type
+IndexedPrism' = Simple . IndexedPrism
+
 
 ------------------------------------------------------------------------------
 -- Utilities for prisms
@@ -53,6 +62,14 @@ public export
 prism' : (b -> s) -> (s -> Maybe a) -> Prism s s a b
 prism' inj prj = prism inj (\x => maybe (Left x) Right (prj x))
 
+public export
+iprism : (b -> t) -> (s -> Either t (i, a)) -> IndexedPrism i s t a b
+iprism inj prj @{_} @{ind} = prism inj prj . indexed @{ind}
+
+public export
+iprism' : (b -> s) -> (s -> Maybe (i, a)) -> IndexedPrism i s s a b
+iprism' inj prj = iprism inj (\x => maybe (Left x) Right (prj x))
+
 
 ||| Extract injection and projection functions from a prism.
 public export

src/Control/Lens/Setter.idr

@@ -7,6 +7,7 @@ import Data.Profunctor.Traversing
 import Data.Profunctor.Mapping
 import Control.Monad.State
 import Control.Lens.Optic
+import Control.Lens.Indexed
 import Control.Lens.Traversal
 
 %default total
@@ -44,6 +45,14 @@ public export
 0 Setter' : (s,a : Type) -> Type
 Setter' = Simple Setter
 
+public export
+0 IndexedSetter : (i,s,t,a,b : Type) -> Type
+IndexedSetter = IndexedOptic IsSetter
+
+public export
+0 IndexedSetter' : (i,s,a : Type) -> Type
+IndexedSetter' = Simple . IndexedSetter
+
 
 ------------------------------------------------------------------------------
 -- Utilities for setters
@@ -55,6 +64,10 @@ public export
 sets : ((a -> b) -> s -> t) -> Setter s t a b
 sets f @{MkIsSetter _} = roam f
 
+public export
+isets : ((i -> a -> b) -> s -> t) -> IndexedSetter i s t a b
+isets f @{MkIsSetter _} @{ind} = roam (f . curry) . indexed @{ind}
+
 ||| Derive a setter from a `Functor` implementation.
 public export
 mapped : Functor f => Setter (f a) (f b) a b
@@ -81,6 +94,17 @@ public export
 (%~) = over
 
 
+public export
+iover : IndexedSetter i s t a b -> (i -> a -> b) -> s -> t
+iover l = l @{MkIsSetter Function} @{Idxed} . uncurry
+
+infixr 4 %@~
+
+public export
+(%@~) : IndexedSetter i s t a b -> (i -> a -> b) -> s -> t
+(%@~) = iover
+
+
 ||| Set the focus or focuses of an optic to a constant value.
 public export
 set : Setter s t a b -> b -> s -> t
@@ -96,15 +120,27 @@ public export
 (.~) = set
 
 
+public export
+iset : IndexedSetter i s t a b -> (i -> b) -> s -> t
+iset l = iover l . (const .)
+
+infix 4 .@~
+
+public export
+(.@~) : IndexedSetter i s t a b -> (i -> b) -> s -> t
+(.@~) = iset
+
+
 ------------------------------------------------------------------------------
--- Operators
+-- More operators
 ------------------------------------------------------------------------------
 
 infixr 4 ?~; infixr 4 <.~; infixr 4 <?~; infixr 4 +~; infixr 4 *~; infixr 4 -~
 infixr 4 /~; infixr 4 ||~; infixr 4 &&~; infixr 4 <+>~
 
-infix 4 %=; infix 4 .=; infix 4 ?=; infix 4 <.=; infix 4 <?=; infix 4 +=
+infix 4 %=; infix 4 %@=; infix 4 .=; infix 4 .@=; infix 4 ?=; infix 4 <.=
-infix 4 *=; infix 4 -=; infix 4 /=; infix 4 ||=; infix 4 &&=; infixr 4 <+>=
+infix 4 <?=; infix 4 +=; infix 4 *=; infix 4 -=; infix 4 /=; infix 4 ||=
+infix 4 &&=; infixr 4 <+>=
 
 infixr 4 <~
 
@@ -175,11 +211,19 @@ public export
 (%=) : MonadState s m => Setter s s a b -> (a -> b) -> m ()
 (%=) = modify .: over
 
+public export
+(%@=) : MonadState s m => IndexedSetter i s s a b -> (i -> a -> b) -> m ()
+(%@=) = modify .: iover
+
 ||| Set the focus of an optic within a state monad.
 public export
 (.=) : MonadState s m => Setter s s a b -> b -> m ()
 (.=) = modify .: set
 
+public export
+(.@=) : MonadState s m => IndexedSetter i s s a b -> (i -> b) -> m ()
+(.@=) = modify .: iset
+
 ||| Set the focus of an optic within a state monad to `Just` a value.
 public export
 (?=) : MonadState s m => Setter s s a (Maybe b) -> b -> m ()

src/Control/Lens/Traversal.idr

@@ -1,12 +1,13 @@
 module Control.Lens.Traversal
 
 import Control.Monad.State
-import Data.Zippable
+import Data.List
 import Data.Profunctor
 import Data.Profunctor.Traversing
 import Control.Applicative.Backwards
 import Control.Applicative.Indexing
 import Control.Lens.Optic
+import Control.Lens.Indexed
 import Control.Lens.Optional
 import Control.Lens.Lens
 import Control.Lens.Prism
@@ -39,17 +40,37 @@ public export
 0 Traversal' : (s,a : Type) -> Type
 Traversal' = Simple Traversal
 
+public export
+0 IndexedTraversal : (i,s,t,a,b : Type) -> Type
+IndexedTraversal = IndexedOptic IsTraversal
+
+public export
+0 IndexedTraversal' : (i,s,a : Type) -> Type
+IndexedTraversal' = Simple . IndexedTraversal
+
 
 ------------------------------------------------------------------------------
 -- Utilities for traversals
 ------------------------------------------------------------------------------
 
 
+public export
+iordinal : Traversal s t a b -> IndexedTraversal Nat s t a b
+iordinal l @{MkIsTraversal _} @{ind} = wander (func . curry) . indexed @{ind}
+  where
+    func : forall f. Applicative f => (Nat -> a -> f b) -> s -> f t
+    func = indexing $ applyStar . l . MkStar {f = Indexing f}
+
+
 ||| Derive a traversal from a `Traversable` implementation.
 public export
 traversed : Traversable t => Traversal (t a) (t b) a b
 traversed @{_} @{MkIsTraversal _} = traverse'
 
+public export
+itraversed : Traversable t => IndexedTraversal Nat (t a) (t b) a b
+itraversed = iordinal traversed
+
 ||| Contstruct a traversal over a `Bitraversable` container with matching types.
 public export
 both : Bitraversable t => Traversal (t a a) (t b b) a b
@@ -71,10 +92,18 @@ public export
 traverseOf : Applicative f => Traversal s t a b -> (a -> f b) -> s -> f t
 traverseOf l = applyStar . l . MkStar {f}
 
+public export
+itraverseOf : Applicative f => IndexedTraversal i s t a b -> (i -> a -> f b) -> s -> f t
+itraverseOf l = traverseOf (l @{%search} @{Idxed}) . uncurry
+
 ||| A version of `traverseOf` but with the arguments flipped.
 public export
 forOf : Applicative f => Traversal s t a b -> s -> (a -> f b) -> f t
-forOf l = flip $ traverseOf l
+forOf = flip . traverseOf
+
+public export
+iforOf : Applicative f => IndexedTraversal i s t a b -> s -> (i -> a -> f b) -> f t
+iforOf = flip . itraverseOf
 
 ||| Evaluate each computation within the traversal and collect the results.
 public export
@@ -128,6 +157,16 @@ failover l f x =
       (b, y) = traverseOf l ((True,) . f) x
   in  guard b $> y
 
+public export
+ifailover : Alternative f => IndexedTraversal i s t a b -> (i -> a -> b) -> s -> f t
+ifailover l = failover (l @{%search} @{Idxed}) . uncurry
+
+
+partsOf_update : a -> State (List a) a
+partsOf_update x = get >>= \case
+  x' :: xs' => put xs' >> pure x'
+  []        => pure x
+
 ||| Convert a traversal into a lens over a list of values.
 |||
 ||| Note that this is only a true lens if the invariant of the list's length is
@@ -136,12 +175,12 @@ failover l f x =
 public export
 partsOf : Traversal s t a a -> Lens s t (List a) (List a)
 partsOf l = lens (runForget $ l $ MkForget pure)
-                  (flip evalState . traverseOf l update)
+                  (flip evalState . traverseOf l partsOf_update)
-  where
+
-    update : a -> State (List a) a
+public export
-    update x = get >>= \case
+ipartsOf : IndexedTraversal i s t a a -> IndexedLens (List i) s t (List a) (List a)
-      x' :: xs' => put xs' >> pure x'
+ipartsOf l = ilens (unzip . (runForget $ l @{%search} @{Idxed} $ MkForget pure))
-      []        => pure x
+                   (flip evalState . itraverseOf l (const partsOf_update))
 
 
 ||| Construct an optional that focuses on the first value of a traversal.

src/Data/Either/Lens.idr

@@ -14,3 +14,13 @@ public export
 Right_ : Prism (Either c a) (Either c b) a b
 Right_ @{MkIsPrism _} = right
 
+
+public export
+chosen : IndexedLens (Either () ()) (Either a a) (Either b b) a b
+chosen = ilens
+  (\case
+    Left x => (Left (), x)
+    Right x => (Right (), x))
+  (\case
+    Left _ => Left
+    Right _ => Right)

src/Data/Tuple/Lens.idr

@@ -14,3 +14,12 @@ fst_ @{MkIsLens _} = first
 public export
 snd_ : Lens (c, a) (c, b) a b
 snd_ @{MkIsLens _} = second
+
+
+public export
+ifst_ : IndexedLens i (a, i) (b, i) a b
+ifst_ = ilens swap (flip $ mapFst . const)
+
+public export
+isnd_ : IndexedLens i (i, a) (i, b) a b
+isnd_ = ilens id (flip $ mapSnd . const)