[ base ] Implement Foldable and Traversable for Identity

CHANGELOG_NEXT.md

@@ -215,6 +215,8 @@ This CHANGELOG describes the merged but unreleased changes. Please see [CHANGELO
 
 * Export `System.Signal.signalCode` and `System.Signal.toSignal`.
 
+* Added implementations of `Foldable` and `Traversable` for `Control.Monad.Identity`
+
 #### Contrib
 
 * `Data.List.Lazy` was moved from `contrib` to `base`.

libs/base/Control/Monad/Identity.idr

@@ -24,6 +24,19 @@ public export
 Monad Identity where
     (Id x) >>= k = k x
 
+public export
+Foldable Identity where
+  foldr f init (Id x) = f x init
+  foldl f init (Id x) = f init x
+  null _ = False
+  foldlM f init (Id x) = f init x
+  toList (Id x) = [x]
+  foldMap f (Id x) = f x
+
+public export
+Traversable Identity where
+  traverse f (Id x) = Id <$> f x
+
 public export
 Show a => Show (Identity a) where
   showPrec d (Id x) = showCon d "Id" $ showArg x