Define cons and snoc optics

src/Control/Lens.idr

@@ -1,6 +1,7 @@
 module Control.Lens
 
 import public Control.Lens.At
+import public Control.Lens.Cons
 import public Control.Lens.Equality
 import public Control.Lens.Fold
 import public Control.Lens.Getter

src/Control/Lens/Cons.idr

@@ -0,0 +1,36 @@
+module Control.Lens.Cons
+
+import Data.Profunctor
+import Control.Lens.Optic
+import Control.Lens.Iso
+import Control.Lens.Prism
+import Control.Lens.Optional
+
+%default total
+
+
+public export
+interface Cons s t a b | s where
+  cons_ : Prism s t (a, s) (b, t)
+
+public export
+head_ : Cons s s a a => Optional' s a
+head_ @{_} @{MkIsOptional _} = cons_ . first
+
+public export
+tail_ : Cons s s a a => Optional' s s
+tail_ @{_} @{MkIsOptional _} = cons_ . second
+
+
+public export
+interface Snoc s t a b | s where
+  snoc_ : Prism s t (s, a) (t, b)
+
+public export
+init_ : Snoc s s a a => Optional' s s
+init_ @{_} @{MkIsOptional _} = snoc_ . first
+
+public export
+last_ : Snoc s s a a => Optional' s a
+last_ @{_} @{MkIsOptional _} = snoc_ . second
+