Add unprotectEff (#9)

CHANGELOG.md

@@ -1,5 +1,6 @@
 # resourcet-effectful-1.0.1.0 (2023-??-??)
-* Add `allocateEff`, `allocateEff_`, `registerEff` and `releaseEff`.
+* Add `allocateEff`, `allocateEff_`, `registerEff`, `releaseEff` and
+  `unprotectEff'.
 * Re-export `ReleaseKey` and `ResourceCleanupException`.
 
 # resourcet-effectful-1.0.0.0 (2022-07-14)

src/Effectful/Resource.hs

@@ -18,6 +18,8 @@ module Effectful.Resource
   , R.register
   , R.release
   , R.unprotect
+  , ReleaseAction(..)
+  , unprotectEff
 
     -- * Internal state
   , R.InternalState
@@ -109,6 +111,22 @@ registerEff release = do
 releaseEff :: Resource :> es => R.ReleaseKey -> Eff es ()
 releaseEff = unsafeEff_ . R.release
 
+-- | Action for releasing a resource.
+newtype ReleaseAction = ReleaseAction
+  { runReleaseAction :: forall es. Resource :> es => Eff es ()
+  }
+
+-- | A variant of 'R.unprotect' adjusted to work in the 'Eff' monad.
+--
+-- /Note:/ if the resource was acquired using 'allocateEff', 'allocateEff_' or
+-- 'registerEff' then the returned 'ReleaseAction' will run in a clone of the
+-- environment it was registered in.
+--
+-- See the documentation of the aforementioned functions for more information.
+unprotectEff :: Resource :> es => R.ReleaseKey -> Eff es (Maybe ReleaseAction)
+unprotectEff key = unsafeEff_ $ do
+  fmap (\m -> ReleaseAction $ unsafeEff_ m) <$> R.unprotect key
+
 ----------------------------------------
 -- Internal state