Add lens module for strings

src/Data/String/Lens.idr

@@ -0,0 +1,30 @@
+module Data.String.Lens
+
+import Data.String
+import Data.Profunctor
+import public Control.Lens
+import Data.List.Lens
+
+%default total
+
+
+public export
+unpacked : Iso' String (List Char)
+unpacked = iso unpack pack
+
+public export
+packed : Iso' (List Char) String
+packed = iso pack unpack
+
+
+public export
+Ixed Nat Char String where
+  ix k = unpacked . ix k
+
+public export
+Cons String String Char Char where
+  cons_ = prism' (uncurry strCons) strUncons
+
+public export
+Snoc String String Char Char where
+  snoc_ = unpacked . snoc_ . mappingFst packed