diff --git a/Control/DeepSeq.hs b/Control/DeepSeq.hs
--- a/Control/DeepSeq.hs
+++ b/Control/DeepSeq.hs
@@ -6,7 +6,7 @@
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE QuantifiedConstraints #-}
-{-# LANGUAGE Safe #-}
+{-# LANGUAGE Trustworthy #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
 
@@ -78,6 +78,7 @@
   ($!!),
   (<$!!>),
   rwhnf,
+  Unit(..),
 
   -- * Liftings of the 'NFData' class
 
@@ -93,7 +94,6 @@
 import Control.Applicative
 import Control.Concurrent (MVar, ThreadId)
 import Control.Exception (MaskingState (..))
-import Data.Array
 import Data.Complex
 import Data.Fixed
 import Data.Functor.Compose
@@ -117,6 +117,8 @@
 import Data.Word
 import Foreign.C.Types
 import Foreign.Ptr
+import GHC.Arr (Array)
+import qualified GHC.Arr
 import GHC.Fingerprint.Type (Fingerprint (..))
 import GHC.Generics
 import GHC.Stack.Types (CallStack (..), SrcLoc (..))
@@ -214,14 +216,19 @@
 deepseq :: NFData a => a -> b -> b
 deepseq a b = rnf a `seq` b
 
--- | the deep analogue of '$!'.  In the expression @f $!! x@, @x@ is
--- fully evaluated before the function @f@ is applied to it.
+-- | The deep analogue of '$!'.  @f $!! x@ fully evaluates @x@
+-- before returning @f x@.
 --
+-- There is no guarantee about the ordering of evaluation.
+-- @f x@ may be evaluated before @x@ is fully evaluated.
+-- To impose an actual order on evaluation, use 'pseq' from
+-- "Control.Parallel" in the @parallel@ package.
+--
 -- @since 1.2.0.0
 ($!!) :: (NFData a) => (a -> b) -> a -> b
 f $!! x = x `deepseq` f x
 
--- | a variant of 'deepseq' that is useful in some circumstances:
+-- | A variant of 'deepseq' that is useful in some circumstances:
 --
 -- > force x = x `deepseq` x
 --
@@ -397,6 +404,45 @@
 rnf2 :: (NFData2 p, NFData a, NFData b) => p a b -> ()
 rnf2 = liftRnf2 rnf rnf
 
+-- | A monoid with @(<>) = seq@.
+--
+-- Its purpose is to allow reducing structures to normal form using
+-- 'foldMap'-like functions.
+--
+-- ==== __Examples__
+--
+-- @
+-- data Three a = Three a a a
+--
+-- instance Foldable Three where
+--   foldMap f (Three x1 x2 x3) = f x1 <> f x2 <> f x3
+--
+-- instance NFData a => NFData (Three a) where
+--   rnf = runUnit . foldMap (Unit . rnf)
+-- @
+--
+-- @
+-- data Tree a b
+--   = NodeA a [Tree a b]
+--   | NodeB b [Tree a b]
+--
+-- foldMapTree :: Monoid m => (a -> m) -> (b -> m) -> Tree a b -> m
+-- foldMapTree f g = go
+--   where
+--     go (NodeA x ts) = f x <> foldMap go ts
+--     go (NodeB y ts) = g y <> foldMap go ts
+--
+-- instance NFData2 Tree where
+--   liftRnf2 r r' = runUnit . foldMapTree (Unit . r) (Unit . r')
+-- @
+newtype Unit = Unit { runUnit :: () }
+
+instance Semigroup Unit where
+  (<>) = seq
+
+instance Monoid Unit where
+  mempty = Unit ()
+
 instance NFData Int where rnf = rwhnf
 
 instance NFData Word where rnf = rwhnf
@@ -583,15 +629,16 @@
 -- We should use MIN_VERSION array(0,5,1,1) but that's not possible.
 -- There isn't an underscore to not break C preprocessor
 instance (NFData a, NFData b) => NFData (Array a b) where
-  rnf x = rnf (bounds x, Data.Array.elems x)
+  rnf x = rnf (GHC.Arr.bounds x, GHC.Arr.elems x)
 
 -- | @since 1.4.3.0
 instance (NFData a) => NFData1 (Array a) where
-  liftRnf r x = rnf (bounds x) `seq` liftRnf r (Data.Array.elems x)
+  liftRnf r x = rnf (GHC.Arr.bounds x) `seq` liftRnf r (GHC.Arr.elems x)
 
 -- | @since 1.4.3.0
 instance NFData2 Array where
-  liftRnf2 r r' x = liftRnf2 r r (bounds x) `seq` liftRnf r' (Data.Array.elems x)
+  liftRnf2 r r' x =
+    liftRnf2 r r (GHC.Arr.bounds x) `seq` liftRnf r' (GHC.Arr.elems x)
 
 -- | @since 1.4.0.0
 instance NFData a => NFData (Down a) where rnf = rnf1
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -4,6 +4,13 @@
 
 
 
+## 1.5.1.0
+
+  * Add Unit monoid with `seq`
+    ([#18](https://github.com/haskell/deepseq/issues/18), [#105](https://github.com/haskell/deepseq/issues/105))
+  * Drop the dependency on `array`
+    ([#102](https://github.com/haskell/deepseq/issues/102), [#107](https://github.com/haskell/deepseq/issues/107))
+
 ## 1.5.0.0
 
   * Add quantified superclasses to NFData(1,2)
diff --git a/deepseq.cabal b/deepseq.cabal
--- a/deepseq.cabal
+++ b/deepseq.cabal
@@ -1,6 +1,6 @@
 cabal-version:  1.12
 name:           deepseq
-version:        1.5.0.0
+version:        1.5.1.0
 -- NOTE: Don't forget to update ./changelog.md
 
 license:        BSD3
@@ -26,8 +26,11 @@
 
 build-type:     Simple
 tested-with:
-  GHC==9.4.3,
-  GHC==9.2.5,
+  GHC==9.10.1,
+  GHC==9.8.2,
+  GHC==9.6.6,
+  GHC==9.4.8,
+  GHC==9.2.8,
   GHC==9.0.2,
   GHC==8.10.7,
   GHC==8.8.4,
@@ -58,8 +61,7 @@
   if impl(ghc >=9.0)
     build-depends: ghc-prim
 
-  build-depends: base       >= 4.12 && < 4.20,
-                 array      >= 0.4 && < 0.6
+  build-depends: base       >= 4.12 && < 4.21
   ghc-options: -Wall
 
   exposed-modules: Control.DeepSeq
@@ -70,7 +72,6 @@
   main-is: Main.hs
   type: exitcode-stdio-1.0
   build-depends:
-    array,
     base,
     deepseq,
     ghc-prim