[ base ] Add modifyRef into the Ref interface

CHANGELOG.md

@@ -251,6 +251,9 @@
 
 * Adds `Data.Vect.foldrImplGoLemma`.
 
+* `Ref` interface from `Data.Ref` inherits `Monad` and was extended by a function
+  for value modification implemented through reading and writing by default.
+
 #### System
 
 * Changes `getNProcessors` to return the number of online processors rather than

libs/base/Data/Ref.idr

@@ -7,11 +7,21 @@ import Control.Monad.State.Interface
 %default total
 
 public export
-interface Ref m r | m where
+interface Monad m => Ref m r | m where
   newRef : {0 a : Type} -> a -> m (r a)
   readRef : {0 a : Type} -> r a -> m a
   writeRef : r a -> a -> m ()
 
+  ||| Updates a value and returns the previous value
+  modifyRef : (a -> a) -> r a -> m a
+  modifyRef f ref = do
+    old <- readRef ref
+    writeRef ref (f old) $> old
+
+public export
+modifyRef_ : Ref m r => (a -> a) -> r a -> m ()
+modifyRef_ = ignore .: modifyRef
+
 export
 HasIO io => Ref io IORef where
   newRef = newIORef