Add Each interface

src/Control/Lens.idr

@@ -2,6 +2,7 @@ module Control.Lens
 
 import public Control.Lens.At
 import public Control.Lens.Cons
+import public Control.Lens.Each
 import public Control.Lens.Equality
 import public Control.Lens.Fold
 import public Control.Lens.Getter

src/Control/Lens/Each.idr

@@ -0,0 +1,34 @@
+module Control.Lens.Each
+
+import Control.Monad.Identity
+import Control.Applicative.Const
+import Control.Lens.Optic
+import Control.Lens.Iso
+import Control.Lens.Lens
+import Control.Lens.Optional
+import Control.Lens.Traversal
+
+%default total
+
+
+||| An interface for accessing every element of a container.
+|||
+||| This can be thought of as a generalized version of `traversed` for
+||| containers that do not have a `Traversable` implementation.
+public export
+interface Each s t a b | s where
+
+  ||| Access every element of a container at the same time.
+  |||
+  ||| This can be thought of as a generalized version of `traversed` for
+  ||| containers that do not have a `Traversable` implementation.
+  each : Traversal s t a b
+
+
+public export
+Each (Identity a) (Identity b) a b where
+  each = Id_
+
+public export
+Each (Const a b) (Const c d) a c where
+  each = Const_

src/Control/Lens/Iso.idr

@@ -4,6 +4,8 @@ import Data.Maybe
 import Data.Contravariant
 import Data.Tensor
 import Data.Profunctor
+import Control.Monad.Identity
+import Control.Applicative.Const
 import Control.Lens.Optic
 import Control.Lens.Equality
 
@@ -145,6 +147,15 @@ non : Eq a => a -> Iso' (Maybe a) a
 non x = iso (fromMaybe x) (\y => guard (x /= y) $> y)
 
 
+public export
+Id_ : Iso (Identity a) (Identity b) a b
+Id_ = iso runIdentity Id
+
+public export
+Const_ : Iso (Const a b) (Const c d) a c
+Const_ = iso runConst MkConst
+
+
 -- Mapping
 
 ||| Lift an isomorphism through a `Functor`.