diff --git a/Data/Vector/Generic/Mutable.hs b/Data/Vector/Generic/Mutable.hs
--- a/Data/Vector/Generic/Mutable.hs
+++ b/Data/Vector/Generic/Mutable.hs
@@ -30,7 +30,7 @@
   -- * Construction
 
   -- ** Initialisation
-  new, unsafeNew, replicate, replicateM, clone,
+  new, unsafeNew, replicate, replicateM, generate, generateM, clone,
 
   -- ** Growing
   grow, unsafeGrow,
@@ -40,9 +40,16 @@
   clear,
 
   -- * Accessing individual elements
-  read, write, modify, swap, exchange,
-  unsafeRead, unsafeWrite, unsafeModify, unsafeSwap, unsafeExchange,
+  read, write, modify, modifyM, swap, exchange,
+  unsafeRead, unsafeWrite, unsafeModify, unsafeModifyM, unsafeSwap, unsafeExchange,
 
+  -- * Folds
+  mapM_, imapM_, forM_, iforM_,
+  foldl, foldl', foldM, foldM',
+  foldr, foldr', foldrM, foldrM',
+  ifoldl, ifoldl', ifoldM, ifoldM',
+  ifoldr, ifoldr', ifoldrM, ifoldrM',
+
   -- * Modifying vectors
   nextPermutation,
 
@@ -71,10 +78,10 @@
 import           Data.Vector.Fusion.Bundle.Size
 import           Data.Vector.Fusion.Util        ( delay_inline )
 
-import Control.Monad.Primitive ( PrimMonad, PrimState )
+import Control.Monad.Primitive ( PrimMonad, PrimState, stToPrim )
 
 import Prelude hiding ( length, null, replicate, reverse, map, read,
-                        take, drop, splitAt, init, tail )
+                        take, drop, splitAt, init, tail, mapM_, foldr, foldl )
 
 #include "vector.h"
 
@@ -616,6 +623,30 @@
 {-# INLINE replicateM #-}
 replicateM n m = munstream (MBundle.replicateM n m)
 
+-- | /O(n)/ Create a mutable vector of the given length (0 if the length is negative)
+-- and fill it with the results of applying the function to each index.
+--
+-- @since 0.12.3.0
+generate :: (PrimMonad m, MVector v a) => Int -> (Int -> a) -> m (v (PrimState m) a)
+{-# INLINE generate #-}
+generate n f = stToPrim $ generateM n (return . f)
+
+-- | /O(n)/ Create a mutable vector of the given length (0 if the length is
+-- negative) and fill it with the results of applying the monadic function to each
+-- index. Iteration starts at index 0.
+--
+-- @since 0.12.3.0
+generateM :: (PrimMonad m, MVector v a) => Int -> (Int -> m a) -> m (v (PrimState m) a)
+{-# INLINE generateM #-}
+generateM n f
+  | n <= 0    = new 0
+  | otherwise = do
+      vec <- new n
+      let loop i | i >= n    = return vec
+                 | otherwise = do unsafeWrite vec i =<< f i
+                                  loop (i + 1)
+      loop 0
+
 -- | Create a copy of a mutable vector.
 clone :: (PrimMonad m, MVector v a) => v (PrimState m) a -> m (v (PrimState m) a)
 {-# INLINE clone #-}
@@ -755,6 +786,14 @@
 modify v f i = BOUNDS_CHECK(checkIndex) "modify" i (length v)
              $ unsafeModify v f i
 
+-- | Modify the element at the given position using a monadic function.
+--
+-- @since 0.12.3.0
+modifyM :: (PrimMonad m, MVector v a) => v (PrimState m) a -> (a -> m a) -> Int -> m ()
+{-# INLINE modifyM #-}
+modifyM v f i = BOUNDS_CHECK(checkIndex) "modifyM" i (length v)
+              $ unsafeModifyM v f i
+
 -- | Swap the elements at the given positions.
 swap :: (PrimMonad m, MVector v a) => v (PrimState m) a -> Int -> Int -> m ()
 {-# INLINE swap #-}
@@ -788,6 +827,15 @@
                    $ basicUnsafeRead v i >>= \x ->
                      basicUnsafeWrite v i (f x)
 
+-- | Modify the element at the given position using a monadic
+-- function. No bounds checks are performed.
+--
+-- @since 0.12.3.0
+unsafeModifyM :: (PrimMonad m, MVector v a) => v (PrimState m) a -> (a -> m a) -> Int -> m ()
+{-# INLINE unsafeModifyM #-}
+unsafeModifyM v f i = UNSAFE_CHECK(checkIndex) "unsafeModifyM" i (length v)
+                    $ stToPrim . basicUnsafeWrite v i =<< f =<< stToPrim (basicUnsafeRead v i)
+
 -- | Swap the elements at the given positions. No bounds checks are performed.
 unsafeSwap :: (PrimMonad m, MVector v a)
                 => v (PrimState m) a -> Int -> Int -> m ()
@@ -810,6 +858,182 @@
                          y <- unsafeRead v i
                          unsafeWrite v i x
                          return y
+
+-- Folds
+-- -----
+
+forI_ :: (Monad m, MVector v a) => v (PrimState m) a -> (Int -> m b) -> m ()
+{-# INLINE forI_ #-}
+forI_ v f = loop 0
+  where
+    loop i | i >= n    = return ()
+           | otherwise = f i >> loop (i + 1)
+    n = length v
+
+-- | /O(n)/ Apply the monadic action to every element of the vector, discarding the results.
+--
+-- @since 0.12.3.0
+mapM_ :: (PrimMonad m, MVector v a) => (a -> m b) -> v (PrimState m) a -> m ()
+{-# INLINE mapM_ #-}
+mapM_ f v = forI_ v $ \i -> f =<< unsafeRead v i
+
+-- | /O(n)/ Apply the monadic action to every element of the vector and its index, discarding the results.
+--
+-- @since 0.12.3.0
+imapM_ :: (PrimMonad m, MVector v a) => (Int -> a -> m b) -> v (PrimState m) a -> m ()
+{-# INLINE imapM_ #-}
+imapM_ f v = forI_ v $ \i -> f i =<< unsafeRead v i
+
+-- | /O(n)/ Apply the monadic action to every element of the vector,
+-- discarding the results. It's same as the @flip mapM_@.
+--
+-- @since 0.12.3.0
+forM_ :: (PrimMonad m, MVector v a) => v (PrimState m) a -> (a -> m b) -> m ()
+{-# INLINE forM_ #-}
+forM_ = flip mapM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector
+-- and its index, discarding the results. It's same as the @flip imapM_@.
+--
+-- @since 0.12.3.0
+iforM_ :: (PrimMonad m, MVector v a) => v (PrimState m) a -> (Int -> a -> m b) -> m ()
+{-# INLINE iforM_ #-}
+iforM_ = flip imapM_
+
+-- | /O(n)/ Pure left fold.
+--
+-- @since 0.12.3.0
+foldl :: (PrimMonad m, MVector v a) => (b -> a -> b) -> b -> v (PrimState m) a -> m b
+{-# INLINE foldl #-}
+foldl f = ifoldl (\b _ -> f b)
+
+-- | /O(n)/ Pure left fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldl' :: (PrimMonad m, MVector v a) => (b -> a -> b) -> b -> v (PrimState m) a -> m b
+{-# INLINE foldl' #-}
+foldl' f = ifoldl' (\b _ -> f b)
+
+-- | /O(n)/ Pure left fold (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldl :: (PrimMonad m, MVector v a) => (b -> Int -> a -> b) -> b -> v (PrimState m) a -> m b
+{-# INLINE ifoldl #-}
+ifoldl f b0 v = stToPrim $ ifoldM (\b i a -> return $ f b i a) b0 v
+
+-- | /O(n)/ Pure left fold with strict accumulator (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldl' :: (PrimMonad m, MVector v a) => (b -> Int -> a -> b) -> b -> v (PrimState m) a -> m b
+{-# INLINE ifoldl' #-}
+ifoldl' f b0 v = stToPrim $ ifoldM' (\b i a -> return $ f b i a) b0 v
+
+-- | /O(n)/ Pure right fold.
+--
+-- @since 0.12.3.0
+foldr :: (PrimMonad m, MVector v a) => (a -> b -> b) -> b -> v (PrimState m) a -> m b
+{-# INLINE foldr #-}
+foldr f = ifoldr (const f)
+
+-- | /O(n)/ Pure right fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldr' :: (PrimMonad m, MVector v a) => (a -> b -> b) -> b -> v (PrimState m) a -> m b
+{-# INLINE foldr' #-}
+foldr' f = ifoldr' (const f)
+
+-- | /O(n)/ Pure right fold (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldr :: (PrimMonad m, MVector v a) => (Int -> a -> b -> b) -> b -> v (PrimState m) a -> m b
+{-# INLINE ifoldr #-}
+ifoldr f b0 v = stToPrim $ ifoldrM (\i a b -> return $ f i a b) b0 v
+
+-- | /O(n)/ Pure right fold with strict accumulator (function applied
+-- to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldr' :: (PrimMonad m, MVector v a) => (Int -> a -> b -> b) -> b -> v (PrimState m) a -> m b
+{-# INLINE ifoldr' #-}
+ifoldr' f b0 v = stToPrim $ ifoldrM' (\i a b -> return $ f i a b) b0 v
+
+-- | /O(n)/ Monadic fold.
+--
+-- @since 0.12.3.0
+foldM :: (PrimMonad m, MVector v a) => (b -> a -> m b) -> b -> v (PrimState m) a -> m b
+{-# INLINE foldM #-}
+foldM f = ifoldM (\x _ -> f x)
+
+-- | /O(n)/ Monadic fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldM' :: (PrimMonad m, MVector v a) => (b -> a -> m b) -> b -> v (PrimState m) a -> m b
+{-# INLINE foldM' #-}
+foldM' f = ifoldM' (\x _ -> f x)
+
+-- | /O(n)/ Monadic fold (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldM :: (PrimMonad m, MVector v a) => (b -> Int -> a -> m b) -> b -> v (PrimState m) a -> m b
+{-# INLINE ifoldM #-}
+ifoldM f b0 v = loop 0 b0
+  where
+    loop i b | i >= n    = return b
+             | otherwise = do a <- unsafeRead v i
+                              loop (i + 1) =<< f b i a
+    n = length v
+
+-- | /O(n)/ Monadic fold with strict accumulator (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldM' :: (PrimMonad m, MVector v a) => (b -> Int -> a -> m b) -> b -> v (PrimState m) a -> m b
+{-# INLINE ifoldM' #-}
+ifoldM' f b0 v = loop 0 b0
+  where
+    loop i !b | i >= n    = return b
+              | otherwise = do a <- unsafeRead v i
+                               loop (i + 1) =<< f b i a
+    n = length v
+
+-- | /O(n)/ Monadic right fold.
+--
+-- @since 0.12.3.0
+foldrM :: (PrimMonad m, MVector v a) => (a -> b -> m b) -> b -> v (PrimState m) a -> m b
+{-# INLINE foldrM #-}
+foldrM f = ifoldrM (const f)
+
+-- | /O(n)/ Monadic right fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldrM' :: (PrimMonad m, MVector v a) => (a -> b -> m b) -> b -> v (PrimState m) a -> m b
+{-# INLINE foldrM' #-}
+foldrM' f = ifoldrM' (const f)
+
+-- | /O(n)/ Monadic right fold (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldrM :: (PrimMonad m, MVector v a) => (Int -> a -> b -> m b) -> b -> v (PrimState m) a -> m b
+{-# INLINE ifoldrM #-}
+ifoldrM f b0 v = loop (n-1) b0
+  where
+    loop i b | i < 0     = return b
+             | otherwise = do a <- unsafeRead v i
+                              loop (i - 1) =<< f i a b
+    n = length v
+
+-- | /O(n)/ Monadic right fold with strict accumulator (action applied
+-- to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldrM' :: (PrimMonad m, MVector v a) => (Int -> a -> b -> m b) -> b -> v (PrimState m) a -> m b
+{-# INLINE ifoldrM' #-}
+ifoldrM' f b0 v = loop (n-1) b0
+  where
+    loop i !b | i < 0     = return b
+              | otherwise = do a <- unsafeRead v i
+                               loop (i - 1) =<< f i a b
+    n = length v
+
 
 -- Filling and copying
 -- -------------------
diff --git a/Data/Vector/Mutable.hs b/Data/Vector/Mutable.hs
--- a/Data/Vector/Mutable.hs
+++ b/Data/Vector/Mutable.hs
@@ -31,7 +31,7 @@
   -- * Construction
 
   -- ** Initialisation
-  new, unsafeNew, replicate, replicateM, clone,
+  new, unsafeNew, replicate, replicateM, generate, generateM, clone,
 
   -- ** Growing
   grow, unsafeGrow,
@@ -40,9 +40,16 @@
   clear,
 
   -- * Accessing individual elements
-  read, write, modify, swap,
-  unsafeRead, unsafeWrite, unsafeModify, unsafeSwap,
+  read, write, modify, modifyM, swap, exchange,
+  unsafeRead, unsafeWrite, unsafeModify, unsafeModifyM, unsafeSwap, unsafeExchange,
 
+  -- * Folds
+  mapM_, imapM_, forM_, iforM_,
+  foldl, foldl', foldM, foldM',
+  foldr, foldr', foldrM, foldrM',
+  ifoldl, ifoldl', ifoldM, ifoldM',
+  ifoldr, ifoldr', ifoldrM, ifoldrM',
+
   -- * Modifying vectors
   nextPermutation,
 
@@ -60,7 +67,7 @@
 import           Control.Monad.Primitive
 
 import Prelude hiding ( length, null, replicate, reverse, read,
-                        take, drop, splitAt, init, tail )
+                        take, drop, splitAt, init, tail, foldr, foldl, mapM_ )
 
 import Data.Typeable ( Typeable )
 
@@ -299,6 +306,23 @@
 {-# INLINE replicateM #-}
 replicateM = G.replicateM
 
+-- | /O(n)/ Create a mutable vector of the given length (0 if the length is negative)
+-- and fill it with the results of applying the function to each index.
+--
+-- @since 0.12.3.0
+generate :: (PrimMonad m) => Int -> (Int -> a) -> m (MVector (PrimState m) a)
+{-# INLINE generate #-}
+generate = G.generate
+
+-- | /O(n)/ Create a mutable vector of the given length (0 if the length is
+-- negative) and fill it with the results of applying the monadic function to each
+-- index. Iteration starts at index 0.
+--
+-- @since 0.12.3.0
+generateM :: (PrimMonad m) => Int -> (Int -> m a) -> m (MVector (PrimState m) a)
+{-# INLINE generateM #-}
+generateM = G.generateM
+
 -- | Create a copy of a mutable vector.
 clone :: PrimMonad m => MVector (PrimState m) a -> m (MVector (PrimState m) a)
 {-# INLINE clone #-}
@@ -382,11 +406,22 @@
 {-# INLINE modify #-}
 modify = G.modify
 
+-- | Modify the element at the given position using a monadic function.
+--
+-- @since 0.12.3.0
+modifyM :: (PrimMonad m) => MVector (PrimState m) a -> (a -> m a) -> Int -> m ()
+{-# INLINE modifyM #-}
+modifyM = G.modifyM
+
 -- | Swap the elements at the given positions.
 swap :: PrimMonad m => MVector (PrimState m) a -> Int -> Int -> m ()
 {-# INLINE swap #-}
 swap = G.swap
 
+-- | Replace the element at the given position and return the old element.
+exchange :: (PrimMonad m) => MVector (PrimState m) a -> Int -> a -> m a
+{-# INLINE exchange #-}
+exchange = G.exchange
 
 -- | Yield the element at the given position. No bounds checks are performed.
 unsafeRead :: PrimMonad m => MVector (PrimState m) a -> Int -> m a
@@ -403,11 +438,25 @@
 {-# INLINE unsafeModify #-}
 unsafeModify = G.unsafeModify
 
+-- | Modify the element at the given position using a monadic
+-- function. No bounds checks are performed.
+--
+-- @since 0.12.3.0
+unsafeModifyM :: (PrimMonad m) => MVector (PrimState m) a -> (a -> m a) -> Int -> m ()
+{-# INLINE unsafeModifyM #-}
+unsafeModifyM = G.unsafeModifyM
+
 -- | Swap the elements at the given positions. No bounds checks are performed.
 unsafeSwap :: PrimMonad m => MVector (PrimState m) a -> Int -> Int -> m ()
 {-# INLINE unsafeSwap #-}
 unsafeSwap = G.unsafeSwap
 
+-- | Replace the element at the given position and return the old element. No
+-- bounds checks are performed.
+unsafeExchange :: (PrimMonad m) => MVector (PrimState m) a -> Int -> a -> m a
+{-# INLINE unsafeExchange #-}
+unsafeExchange = G.unsafeExchange
+
 -- Filling and copying
 -- -------------------
 
@@ -463,6 +512,154 @@
 nextPermutation :: (PrimMonad m,Ord e) => MVector (PrimState m) e -> m Bool
 {-# INLINE nextPermutation #-}
 nextPermutation = G.nextPermutation
+
+
+-- Folds
+-- -----
+
+-- | /O(n)/ Apply the monadic action to every element of the vector, discarding the results.
+--
+-- @since 0.12.3.0
+mapM_ :: (PrimMonad m) => (a -> m b) -> MVector (PrimState m) a -> m ()
+{-# INLINE mapM_ #-}
+mapM_ = G.mapM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector and its index, discarding the results.
+--
+-- @since 0.12.3.0
+imapM_ :: (PrimMonad m) => (Int -> a -> m b) -> MVector (PrimState m) a -> m ()
+{-# INLINE imapM_ #-}
+imapM_ = G.imapM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector,
+-- discarding the results. It's same as the @flip mapM_@.
+--
+-- @since 0.12.3.0
+forM_ :: (PrimMonad m) => MVector (PrimState m) a -> (a -> m b) -> m ()
+{-# INLINE forM_ #-}
+forM_ = G.forM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector
+-- and its index, discarding the results. It's same as the @flip imapM_@.
+--
+-- @since 0.12.3.0
+iforM_ :: (PrimMonad m) => MVector (PrimState m) a -> (Int -> a -> m b) -> m ()
+{-# INLINE iforM_ #-}
+iforM_ = G.iforM_
+
+-- | /O(n)/ Pure left fold.
+--
+-- @since 0.12.3.0
+foldl :: (PrimMonad m) => (b -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldl #-}
+foldl = G.foldl
+
+-- | /O(n)/ Pure left fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldl' :: (PrimMonad m) => (b -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldl' #-}
+foldl' = G.foldl'
+
+-- | /O(n)/ Pure left fold (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldl :: (PrimMonad m) => (b -> Int -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldl #-}
+ifoldl = G.ifoldl
+
+-- | /O(n)/ Pure left fold with strict accumulator (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldl' :: (PrimMonad m) => (b -> Int -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldl' #-}
+ifoldl' = G.ifoldl'
+
+-- | /O(n)/ Pure right fold.
+--
+-- @since 0.12.3.0
+foldr :: (PrimMonad m) => (a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldr #-}
+foldr = G.foldr
+
+-- | /O(n)/ Pure right fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldr' :: (PrimMonad m) => (a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldr' #-}
+foldr' = G.foldr'
+
+-- | /O(n)/ Pure right fold (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldr :: (PrimMonad m) => (Int -> a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldr #-}
+ifoldr = G.ifoldr
+
+-- | /O(n)/ Pure right fold with strict accumulator (function applied
+-- to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldr' :: (PrimMonad m) => (Int -> a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldr' #-}
+ifoldr' = G.ifoldr'
+
+-- | /O(n)/ Monadic fold.
+--
+-- @since 0.12.3.0
+foldM :: (PrimMonad m) => (b -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldM #-}
+foldM = G.foldM
+
+-- | /O(n)/ Monadic fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldM' :: (PrimMonad m) => (b -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldM' #-}
+foldM' = G.foldM'
+
+-- | /O(n)/ Monadic fold (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldM :: (PrimMonad m) => (b -> Int -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldM #-}
+ifoldM = G.ifoldM
+
+-- | /O(n)/ Monadic fold with strict accumulator (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldM' :: (PrimMonad m) => (b -> Int -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldM' #-}
+ifoldM' = G.ifoldM'
+
+-- | /O(n)/ Monadic right fold.
+--
+-- @since 0.12.3.0
+foldrM :: (PrimMonad m) => (a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldrM #-}
+foldrM = G.foldrM
+
+-- | /O(n)/ Monadic right fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldrM' :: (PrimMonad m) => (a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldrM' #-}
+foldrM' = G.foldrM'
+
+-- | /O(n)/ Monadic right fold (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldrM :: (PrimMonad m) => (Int -> a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldrM #-}
+ifoldrM = G.ifoldrM
+
+-- | /O(n)/ Monadic right fold with strict accumulator (action applied
+-- to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldrM' :: (PrimMonad m) => (Int -> a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldrM' #-}
+ifoldrM' = G.ifoldrM'
 
 -- Conversions - Arrays
 -- -----------------------------
diff --git a/Data/Vector/Primitive/Mutable.hs b/Data/Vector/Primitive/Mutable.hs
--- a/Data/Vector/Primitive/Mutable.hs
+++ b/Data/Vector/Primitive/Mutable.hs
@@ -31,7 +31,7 @@
   -- * Construction
 
   -- ** Initialisation
-  new, unsafeNew, replicate, replicateM, clone,
+  new, unsafeNew, replicate, replicateM, generate, generateM, clone,
 
   -- ** Growing
   grow, unsafeGrow,
@@ -40,9 +40,16 @@
   clear,
 
   -- * Accessing individual elements
-  read, write, modify, swap,
-  unsafeRead, unsafeWrite, unsafeModify, unsafeSwap,
+  read, write, modify, modifyM, swap, exchange,
+  unsafeRead, unsafeWrite, unsafeModify, unsafeModifyM, unsafeSwap, unsafeExchange,
 
+  -- * Folds
+  mapM_, imapM_, forM_, iforM_,
+  foldl, foldl', foldM, foldM',
+  foldr, foldr', foldrM, foldrM',
+  ifoldl, ifoldl', ifoldM, ifoldM',
+  ifoldr, ifoldr', ifoldrM, ifoldrM',
+
   -- * Modifying vectors
   nextPermutation,
 
@@ -64,7 +71,7 @@
                        )
 
 import Prelude hiding ( length, null, replicate, reverse, map, read,
-                        take, drop, splitAt, init, tail )
+                        take, drop, splitAt, init, tail, foldr, foldl, mapM_ )
 
 import Data.Typeable ( Typeable )
 
@@ -247,6 +254,23 @@
 {-# INLINE replicateM #-}
 replicateM = G.replicateM
 
+-- | /O(n)/ Create a mutable vector of the given length (0 if the length is negative)
+-- and fill it with the results of applying the function to each index.
+--
+-- @since 0.12.3.0
+generate :: (PrimMonad m, Prim a) => Int -> (Int -> a) -> m (MVector (PrimState m) a)
+{-# INLINE generate #-}
+generate = G.generate
+
+-- | /O(n)/ Create a mutable vector of the given length (0 if the length is
+-- negative) and fill it with the results of applying the monadic function to each
+-- index. Iteration starts at index 0.
+--
+-- @since 0.12.3.0
+generateM :: (PrimMonad m, Prim a) => Int -> (Int -> m a) -> m (MVector (PrimState m) a)
+{-# INLINE generateM #-}
+generateM = G.generateM
+
 -- | Create a copy of a mutable vector.
 clone :: (PrimMonad m, Prim a)
       => MVector (PrimState m) a -> m (MVector (PrimState m) a)
@@ -332,11 +356,22 @@
 {-# INLINE modify #-}
 modify = G.modify
 
+-- | Modify the element at the given position using a monadic function.
+--
+-- @since 0.12.3.0
+modifyM :: (PrimMonad m, Prim a) => MVector (PrimState m) a -> (a -> m a) -> Int -> m ()
+{-# INLINE modifyM #-}
+modifyM = G.modifyM
+
 -- | Swap the elements at the given positions.
 swap :: (PrimMonad m, Prim a) => MVector (PrimState m) a -> Int -> Int -> m ()
 {-# INLINE swap #-}
 swap = G.swap
 
+-- | Replace the element at the given position and return the old element.
+exchange :: (PrimMonad m, Prim a) => MVector (PrimState m) a -> Int -> a -> m a
+{-# INLINE exchange #-}
+exchange = G.exchange
 
 -- | Yield the element at the given position. No bounds checks are performed.
 unsafeRead :: (PrimMonad m, Prim a) => MVector (PrimState m) a -> Int -> m a
@@ -354,12 +389,26 @@
 {-# INLINE unsafeModify #-}
 unsafeModify = G.unsafeModify
 
+-- | Modify the element at the given position using a monadic
+-- function. No bounds checks are performed.
+--
+-- @since 0.12.3.0
+unsafeModifyM :: (PrimMonad m, Prim a) => MVector (PrimState m) a -> (a -> m a) -> Int -> m ()
+{-# INLINE unsafeModifyM #-}
+unsafeModifyM = G.unsafeModifyM
+
 -- | Swap the elements at the given positions. No bounds checks are performed.
 unsafeSwap
     :: (PrimMonad m, Prim a) => MVector (PrimState m) a -> Int -> Int -> m ()
 {-# INLINE unsafeSwap #-}
 unsafeSwap = G.unsafeSwap
 
+-- | Replace the element at the given position and return the old element. No
+-- bounds checks are performed.
+unsafeExchange :: (PrimMonad m, Prim a) => MVector (PrimState m) a -> Int -> a -> m a
+{-# INLINE unsafeExchange #-}
+unsafeExchange = G.unsafeExchange
+
 -- Filling and copying
 -- -------------------
 
@@ -419,3 +468,151 @@
 nextPermutation :: (PrimMonad m,Ord e,Prim e) => MVector (PrimState m) e -> m Bool
 {-# INLINE nextPermutation #-}
 nextPermutation = G.nextPermutation
+
+
+-- Folds
+-- -----
+
+-- | /O(n)/ Apply the monadic action to every element of the vector, discarding the results.
+--
+-- @since 0.12.3.0
+mapM_ :: (PrimMonad m, Prim a) => (a -> m b) -> MVector (PrimState m) a -> m ()
+{-# INLINE mapM_ #-}
+mapM_ = G.mapM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector and its index, discarding the results.
+--
+-- @since 0.12.3.0
+imapM_ :: (PrimMonad m, Prim a) => (Int -> a -> m b) -> MVector (PrimState m) a -> m ()
+{-# INLINE imapM_ #-}
+imapM_ = G.imapM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector,
+-- discarding the results. It's same as the @flip mapM_@.
+--
+-- @since 0.12.3.0
+forM_ :: (PrimMonad m, Prim a) => MVector (PrimState m) a -> (a -> m b) -> m ()
+{-# INLINE forM_ #-}
+forM_ = G.forM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector
+-- and its index, discarding the results. It's same as the @flip imapM_@.
+--
+-- @since 0.12.3.0
+iforM_ :: (PrimMonad m, Prim a) => MVector (PrimState m) a -> (Int -> a -> m b) -> m ()
+{-# INLINE iforM_ #-}
+iforM_ = G.iforM_
+
+-- | /O(n)/ Pure left fold.
+--
+-- @since 0.12.3.0
+foldl :: (PrimMonad m, Prim a) => (b -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldl #-}
+foldl = G.foldl
+
+-- | /O(n)/ Pure left fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldl' :: (PrimMonad m, Prim a) => (b -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldl' #-}
+foldl' = G.foldl'
+
+-- | /O(n)/ Pure left fold (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldl :: (PrimMonad m, Prim a) => (b -> Int -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldl #-}
+ifoldl = G.ifoldl
+
+-- | /O(n)/ Pure left fold with strict accumulator (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldl' :: (PrimMonad m, Prim a) => (b -> Int -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldl' #-}
+ifoldl' = G.ifoldl'
+
+-- | /O(n)/ Pure right fold.
+--
+-- @since 0.12.3.0
+foldr :: (PrimMonad m, Prim a) => (a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldr #-}
+foldr = G.foldr
+
+-- | /O(n)/ Pure right fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldr' :: (PrimMonad m, Prim a) => (a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldr' #-}
+foldr' = G.foldr'
+
+-- | /O(n)/ Pure right fold (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldr :: (PrimMonad m, Prim a) => (Int -> a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldr #-}
+ifoldr = G.ifoldr
+
+-- | /O(n)/ Pure right fold with strict accumulator (function applied
+-- to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldr' :: (PrimMonad m, Prim a) => (Int -> a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldr' #-}
+ifoldr' = G.ifoldr'
+
+-- | /O(n)/ Monadic fold.
+--
+-- @since 0.12.3.0
+foldM :: (PrimMonad m, Prim a) => (b -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldM #-}
+foldM = G.foldM
+
+-- | /O(n)/ Monadic fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldM' :: (PrimMonad m, Prim a) => (b -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldM' #-}
+foldM' = G.foldM'
+
+-- | /O(n)/ Monadic fold (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldM :: (PrimMonad m, Prim a) => (b -> Int -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldM #-}
+ifoldM = G.ifoldM
+
+-- | /O(n)/ Monadic fold with strict accumulator (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldM' :: (PrimMonad m, Prim a) => (b -> Int -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldM' #-}
+ifoldM' = G.ifoldM'
+
+-- | /O(n)/ Monadic right fold.
+--
+-- @since 0.12.3.0
+foldrM :: (PrimMonad m, Prim a) => (a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldrM #-}
+foldrM = G.foldrM
+
+-- | /O(n)/ Monadic right fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldrM' :: (PrimMonad m, Prim a) => (a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldrM' #-}
+foldrM' = G.foldrM'
+
+-- | /O(n)/ Monadic right fold (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldrM :: (PrimMonad m, Prim a) => (Int -> a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldrM #-}
+ifoldrM = G.ifoldrM
+
+-- | /O(n)/ Monadic right fold with strict accumulator (action applied
+-- to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldrM' :: (PrimMonad m, Prim a) => (Int -> a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldrM' #-}
+ifoldrM' = G.ifoldrM'
diff --git a/Data/Vector/Storable.hs b/Data/Vector/Storable.hs
--- a/Data/Vector/Storable.hs
+++ b/Data/Vector/Storable.hs
@@ -255,14 +255,14 @@
   {-# INLINE basicUnsafeIndexM #-}
   basicUnsafeIndexM (Vector _ fp) i = return
                                     . unsafeInlineIO
-                                    $ withForeignPtr fp $ \p ->
+                                    $ unsafeWithForeignPtr fp $ \p ->
                                       peekElemOff p i
 
   {-# INLINE basicUnsafeCopy #-}
   basicUnsafeCopy (MVector n fp) (Vector _ fq)
     = unsafePrimToPrim
-    $ withForeignPtr fp $ \p ->
-      withForeignPtr fq $ \q ->
+    $ unsafeWithForeignPtr fp $ \p ->
+      unsafeWithForeignPtr fq $ \q ->
       copyArray p q n
 
   {-# INLINE elemseq #-}
diff --git a/Data/Vector/Storable/Internal.hs b/Data/Vector/Storable/Internal.hs
--- a/Data/Vector/Storable/Internal.hs
+++ b/Data/Vector/Storable/Internal.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP #-}
+
 -- |
 -- Module      : Data.Vector.Storable.Internal
 -- Copyright   : (c) Roman Leshchinskiy 2009-2010
@@ -11,12 +13,17 @@
 --
 
 module Data.Vector.Storable.Internal (
-  getPtr, setPtr, updPtr
+  getPtr, setPtr, updPtr, unsafeWithForeignPtr
 ) where
 
 import Foreign.ForeignPtr ()
 import Foreign.Ptr        ()
 import GHC.ForeignPtr   ( ForeignPtr(..) )
+#if MIN_VERSION_base(4,15,0)
+import GHC.ForeignPtr       ( unsafeWithForeignPtr )
+#else
+import Foreign.ForeignPtr   ( withForeignPtr )
+#endif
 import GHC.Ptr          ( Ptr(..) )
 
 getPtr :: ForeignPtr a -> Ptr a
@@ -31,3 +38,12 @@
 {-# INLINE updPtr #-}
 updPtr f (ForeignPtr p c) = case f (Ptr p) of { Ptr q -> ForeignPtr q c }
 
+#if !MIN_VERSION_base(4,15,0)
+-- | A compatibility wrapper for 'GHC.ForeignPtr.unsafeWithForeignPtr' provided
+-- by GHC 9.0.1 and later.
+--
+-- Only to be used when the continuation is known not to
+-- unconditionally diverge lest unsoundness can result.
+unsafeWithForeignPtr :: ForeignPtr a -> (Ptr a -> IO b) -> IO b
+unsafeWithForeignPtr = withForeignPtr
+#endif
diff --git a/Data/Vector/Storable/Mutable.hs b/Data/Vector/Storable/Mutable.hs
--- a/Data/Vector/Storable/Mutable.hs
+++ b/Data/Vector/Storable/Mutable.hs
@@ -33,7 +33,7 @@
   -- * Construction
 
   -- ** Initialisation
-  new, unsafeNew, replicate, replicateM, clone,
+  new, unsafeNew, replicate, replicateM, generate, generateM, clone,
 
   -- ** Growing
   grow, unsafeGrow,
@@ -42,10 +42,18 @@
   clear,
 
   -- * Accessing individual elements
-  read, write, modify, swap,
-  unsafeRead, unsafeWrite, unsafeModify, unsafeSwap,
+  read, write, modify, modifyM, swap, exchange,
+  unsafeRead, unsafeWrite, unsafeModify, unsafeModifyM, unsafeSwap, unsafeExchange,
 
+  -- * Folds
+  mapM_, imapM_, forM_, iforM_,
+  foldl, foldl', foldM, foldM',
+  foldr, foldr', foldrM, foldrM',
+  ifoldl, ifoldl', ifoldM, ifoldM',
+  ifoldr, ifoldr', ifoldrM, ifoldrM',
+
   -- * Modifying vectors
+  nextPermutation,
 
   -- ** Filling and copying
   set, copy, move, unsafeCopy, unsafeMove,
@@ -94,7 +102,7 @@
 import GHC.Ptr (Ptr(..))
 
 import Prelude hiding ( length, null, replicate, reverse, map, read,
-                        take, drop, splitAt, init, tail )
+                        take, drop, splitAt, init, tail, foldr, foldl, mapM_ )
 
 import Data.Typeable ( Typeable )
 
@@ -154,12 +162,12 @@
   {-# INLINE basicUnsafeRead #-}
   basicUnsafeRead (MVector _ fp) i
     = unsafePrimToPrim
-    $ withForeignPtr fp (`peekElemOff` i)
+    $ unsafeWithForeignPtr fp (`peekElemOff` i)
 
   {-# INLINE basicUnsafeWrite #-}
   basicUnsafeWrite (MVector _ fp) i x
     = unsafePrimToPrim
-    $ withForeignPtr fp $ \p -> pokeElemOff p i x
+    $ unsafeWithForeignPtr fp $ \p -> pokeElemOff p i x
 
   {-# INLINE basicSet #-}
   basicSet = storableSet
@@ -167,20 +175,20 @@
   {-# INLINE basicUnsafeCopy #-}
   basicUnsafeCopy (MVector n fp) (MVector _ fq)
     = unsafePrimToPrim
-    $ withForeignPtr fp $ \p ->
-      withForeignPtr fq $ \q ->
+    $ unsafeWithForeignPtr fp $ \p ->
+      unsafeWithForeignPtr fq $ \q ->
       copyArray p q n
 
   {-# INLINE basicUnsafeMove #-}
   basicUnsafeMove (MVector n fp) (MVector _ fq)
     = unsafePrimToPrim
-    $ withForeignPtr fp $ \p ->
-      withForeignPtr fq $ \q ->
+    $ unsafeWithForeignPtr fp $ \p ->
+      unsafeWithForeignPtr fq $ \q ->
       moveArray p q n
 
 storableZero :: forall a m. (Storable a, PrimMonad m) => MVector (PrimState m) a -> m ()
 {-# INLINE storableZero #-}
-storableZero (MVector n fp) = unsafePrimToPrim . withForeignPtr fp $ \ptr-> do
+storableZero (MVector n fp) = unsafePrimToPrim . unsafeWithForeignPtr fp $ \ptr-> do
   memsetPrimPtr_vector (castPtr ptr) byteSize (0 :: Word8)
  where
  x :: a
@@ -198,7 +206,7 @@
                   2 -> storableSetAsPrim n fp x (undefined :: Word16)
                   4 -> storableSetAsPrim n fp x (undefined :: Word32)
                   8 -> storableSetAsPrim n fp x (undefined :: Word64)
-                  _ -> withForeignPtr fp $ \p -> do
+                  _ -> unsafeWithForeignPtr fp $ \p -> do
                        poke p x
 
                        let do_set i
@@ -212,7 +220,7 @@
 storableSetAsPrim
   :: forall a b . (Storable a, Prim b) => Int -> ForeignPtr a -> a -> b -> IO ()
 {-# INLINE [0] storableSetAsPrim #-}
-storableSetAsPrim n fp x _y = withForeignPtr fp $ \ ptr  -> do
+storableSetAsPrim n fp x _y = unsafeWithForeignPtr fp $ \ ptr  -> do
     poke ptr x
      -- we dont equate storable and prim reps, so we need to write to a slot
      -- in storable
@@ -375,6 +383,23 @@
 {-# INLINE replicateM #-}
 replicateM = G.replicateM
 
+-- | /O(n)/ Create a mutable vector of the given length (0 if the length is negative)
+-- and fill it with the results of applying the function to each index.
+--
+-- @since 0.12.3.0
+generate :: (PrimMonad m, Storable a) => Int -> (Int -> a) -> m (MVector (PrimState m) a)
+{-# INLINE generate #-}
+generate = G.generate
+
+-- | /O(n)/ Create a mutable vector of the given length (0 if the length is
+-- negative) and fill it with the results of applying the monadic function to each
+-- index. Iteration starts at index 0.
+--
+-- @since 0.12.3.0
+generateM :: (PrimMonad m, Storable a) => Int -> (Int -> m a) -> m (MVector (PrimState m) a)
+{-# INLINE generateM #-}
+generateM = G.generateM
+
 -- | Create a copy of a mutable vector.
 clone :: (PrimMonad m, Storable a)
       => MVector (PrimState m) a -> m (MVector (PrimState m) a)
@@ -461,12 +486,23 @@
 {-# INLINE modify #-}
 modify = G.modify
 
+-- | Modify the element at the given position using a monadic function.
+--
+-- @since 0.12.3.0
+modifyM :: (PrimMonad m, Storable a) => MVector (PrimState m) a -> (a -> m a) -> Int -> m ()
+{-# INLINE modifyM #-}
+modifyM = G.modifyM
+
 -- | Swap the elements at the given positions.
 swap
     :: (PrimMonad m, Storable a) => MVector (PrimState m) a -> Int -> Int -> m ()
 {-# INLINE swap #-}
 swap = G.swap
 
+-- | Replace the element at the given position and return the old element.
+exchange :: (PrimMonad m, Storable a) => MVector (PrimState m) a -> Int -> a -> m a
+{-# INLINE exchange #-}
+exchange = G.exchange
 
 -- | Yield the element at the given position. No bounds checks are performed.
 unsafeRead :: (PrimMonad m, Storable a) => MVector (PrimState m) a -> Int -> m a
@@ -484,12 +520,26 @@
 {-# INLINE unsafeModify #-}
 unsafeModify = G.unsafeModify
 
+-- | Modify the element at the given position using a monadic
+-- function. No bounds checks are performed.
+--
+-- @since 0.12.3.0
+unsafeModifyM :: (PrimMonad m, Storable a) => MVector (PrimState m) a -> (a -> m a) -> Int -> m ()
+{-# INLINE unsafeModifyM #-}
+unsafeModifyM = G.unsafeModifyM
+
 -- | Swap the elements at the given positions. No bounds checks are performed.
 unsafeSwap
     :: (PrimMonad m, Storable a) => MVector (PrimState m) a -> Int -> Int -> m ()
 {-# INLINE unsafeSwap #-}
 unsafeSwap = G.unsafeSwap
 
+-- | Replace the element at the given position and return the old element. No
+-- bounds checks are performed.
+unsafeExchange :: (PrimMonad m, Storable a) => MVector (PrimState m) a -> Int -> a -> m a
+{-# INLINE unsafeExchange #-}
+unsafeExchange = G.unsafeExchange
+
 -- Filling and copying
 -- -------------------
 
@@ -543,6 +593,161 @@
            -> m ()
 {-# INLINE unsafeMove #-}
 unsafeMove = G.unsafeMove
+
+-- | Compute the next (lexicographically) permutation of given vector in-place.
+--   Returns False when input is the last permutation
+nextPermutation :: (PrimMonad m, Storable e, Ord e) => MVector (PrimState m) e -> m Bool
+{-# INLINE nextPermutation #-}
+nextPermutation = G.nextPermutation
+
+
+-- Folds
+-- -----
+
+-- | /O(n)/ Apply the monadic action to every element of the vector, discarding the results.
+--
+-- @since 0.12.3.0
+mapM_ :: (PrimMonad m, Storable a) => (a -> m b) -> MVector (PrimState m) a -> m ()
+{-# INLINE mapM_ #-}
+mapM_ = G.mapM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector and its index, discarding the results.
+--
+-- @since 0.12.3.0
+imapM_ :: (PrimMonad m, Storable a) => (Int -> a -> m b) -> MVector (PrimState m) a -> m ()
+{-# INLINE imapM_ #-}
+imapM_ = G.imapM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector,
+-- discarding the results. It's same as the @flip mapM_@.
+--
+-- @since 0.12.3.0
+forM_ :: (PrimMonad m, Storable a) => MVector (PrimState m) a -> (a -> m b) -> m ()
+{-# INLINE forM_ #-}
+forM_ = G.forM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector
+-- and its index, discarding the results. It's same as the @flip imapM_@.
+--
+-- @since 0.12.3.0
+iforM_ :: (PrimMonad m, Storable a) => MVector (PrimState m) a -> (Int -> a -> m b) -> m ()
+{-# INLINE iforM_ #-}
+iforM_ = G.iforM_
+
+-- | /O(n)/ Pure left fold.
+--
+-- @since 0.12.3.0
+foldl :: (PrimMonad m, Storable a) => (b -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldl #-}
+foldl = G.foldl
+
+-- | /O(n)/ Pure left fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldl' :: (PrimMonad m, Storable a) => (b -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldl' #-}
+foldl' = G.foldl'
+
+-- | /O(n)/ Pure left fold (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldl :: (PrimMonad m, Storable a) => (b -> Int -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldl #-}
+ifoldl = G.ifoldl
+
+-- | /O(n)/ Pure left fold with strict accumulator (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldl' :: (PrimMonad m, Storable a) => (b -> Int -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldl' #-}
+ifoldl' = G.ifoldl'
+
+-- | /O(n)/ Pure right fold.
+--
+-- @since 0.12.3.0
+foldr :: (PrimMonad m, Storable a) => (a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldr #-}
+foldr = G.foldr
+
+-- | /O(n)/ Pure right fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldr' :: (PrimMonad m, Storable a) => (a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldr' #-}
+foldr' = G.foldr'
+
+-- | /O(n)/ Pure right fold (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldr :: (PrimMonad m, Storable a) => (Int -> a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldr #-}
+ifoldr = G.ifoldr
+
+-- | /O(n)/ Pure right fold with strict accumulator (function applied
+-- to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldr' :: (PrimMonad m, Storable a) => (Int -> a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldr' #-}
+ifoldr' = G.ifoldr'
+
+-- | /O(n)/ Monadic fold.
+--
+-- @since 0.12.3.0
+foldM :: (PrimMonad m, Storable a) => (b -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldM #-}
+foldM = G.foldM
+
+-- | /O(n)/ Monadic fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldM' :: (PrimMonad m, Storable a) => (b -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldM' #-}
+foldM' = G.foldM'
+
+-- | /O(n)/ Monadic fold (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldM :: (PrimMonad m, Storable a) => (b -> Int -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldM #-}
+ifoldM = G.ifoldM
+
+-- | /O(n)/ Monadic fold with strict accumulator (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldM' :: (PrimMonad m, Storable a) => (b -> Int -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldM' #-}
+ifoldM' = G.ifoldM'
+
+-- | /O(n)/ Monadic right fold.
+--
+-- @since 0.12.3.0
+foldrM :: (PrimMonad m, Storable a) => (a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldrM #-}
+foldrM = G.foldrM
+
+-- | /O(n)/ Monadic right fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldrM' :: (PrimMonad m, Storable a) => (a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldrM' #-}
+foldrM' = G.foldrM'
+
+-- | /O(n)/ Monadic right fold (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldrM :: (PrimMonad m, Storable a) => (Int -> a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldrM #-}
+ifoldrM = G.ifoldrM
+
+-- | /O(n)/ Monadic right fold with strict accumulator (action applied
+-- to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldrM' :: (PrimMonad m, Storable a) => (Int -> a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldrM' #-}
+ifoldrM' = G.ifoldrM'
+
 
 -- Unsafe conversions
 -- ------------------
diff --git a/Data/Vector/Unboxed/Mutable.hs b/Data/Vector/Unboxed/Mutable.hs
--- a/Data/Vector/Unboxed/Mutable.hs
+++ b/Data/Vector/Unboxed/Mutable.hs
@@ -31,7 +31,7 @@
   -- * Construction
 
   -- ** Initialisation
-  new, unsafeNew, replicate, replicateM, clone,
+  new, unsafeNew, replicate, replicateM, generate, generateM, clone,
 
   -- ** Growing
   grow, unsafeGrow,
@@ -44,9 +44,16 @@
   unzip, unzip3, unzip4, unzip5, unzip6,
 
   -- * Accessing individual elements
-  read, write, modify, swap,
-  unsafeRead, unsafeWrite, unsafeModify, unsafeSwap,
+  read, write, modify, modifyM, swap, exchange,
+  unsafeRead, unsafeWrite, unsafeModify, unsafeModifyM, unsafeSwap, unsafeExchange,
 
+  -- * Folds
+  mapM_, imapM_, forM_, iforM_,
+  foldl, foldl', foldM, foldM',
+  foldr, foldr', foldrM, foldrM',
+  ifoldl, ifoldl', ifoldM, ifoldM',
+  ifoldr, ifoldr', ifoldrM, ifoldrM',
+
   -- * Modifying vectors
   nextPermutation,
 
@@ -61,7 +68,7 @@
 
 import Prelude hiding ( length, null, replicate, reverse, map, read,
                         take, drop, splitAt, init, tail,
-                        zip, zip3, unzip, unzip3 )
+                        zip, zip3, unzip, unzip3, foldr, foldl, mapM_ )
 
 -- don't import an unused Data.Vector.Internal.Check
 #define NOT_VECTOR_MODULE
@@ -176,6 +183,23 @@
 {-# INLINE replicateM #-}
 replicateM = G.replicateM
 
+-- | /O(n)/ Create a mutable vector of the given length (0 if the length is negative)
+-- and fill it with the results of applying the function to each index.
+--
+-- @since 0.12.3.0
+generate :: (PrimMonad m, Unbox a) => Int -> (Int -> a) -> m (MVector (PrimState m) a)
+{-# INLINE generate #-}
+generate = G.generate
+
+-- | /O(n)/ Create a mutable vector of the given length (0 if the length is
+-- negative) and fill it with the results of applying the monadic function to each
+-- index. Iteration starts at index 0.
+--
+-- @since 0.12.3.0
+generateM :: (PrimMonad m, Unbox a) => Int -> (Int -> m a) -> m (MVector (PrimState m) a)
+{-# INLINE generateM #-}
+generateM = G.generateM
+
 -- | Create a copy of a mutable vector.
 clone :: (PrimMonad m, Unbox a)
       => MVector (PrimState m) a -> m (MVector (PrimState m) a)
@@ -261,11 +285,22 @@
 {-# INLINE modify #-}
 modify = G.modify
 
+-- | Modify the element at the given position using a monadic function.
+--
+-- @since 0.12.3.0
+modifyM :: (PrimMonad m, Unbox a) => MVector (PrimState m) a -> (a -> m a) -> Int -> m ()
+{-# INLINE modifyM #-}
+modifyM = G.modifyM
+
 -- | Swap the elements at the given positions.
 swap :: (PrimMonad m, Unbox a) => MVector (PrimState m) a -> Int -> Int -> m ()
 {-# INLINE swap #-}
 swap = G.swap
 
+-- | Replace the element at the given position and return the old element.
+exchange :: (PrimMonad m, Unbox a) => MVector (PrimState m) a -> Int -> a -> m a
+{-# INLINE exchange #-}
+exchange = G.exchange
 
 -- | Yield the element at the given position. No bounds checks are performed.
 unsafeRead :: (PrimMonad m, Unbox a) => MVector (PrimState m) a -> Int -> m a
@@ -283,12 +318,26 @@
 {-# INLINE unsafeModify #-}
 unsafeModify = G.unsafeModify
 
+-- | Modify the element at the given position using a monadic
+-- function. No bounds checks are performed.
+--
+-- @since 0.12.3.0
+unsafeModifyM :: (PrimMonad m, Unbox a) => MVector (PrimState m) a -> (a -> m a) -> Int -> m ()
+{-# INLINE unsafeModifyM #-}
+unsafeModifyM = G.unsafeModifyM
+
 -- | Swap the elements at the given positions. No bounds checks are performed.
 unsafeSwap
     :: (PrimMonad m, Unbox a) => MVector (PrimState m) a -> Int -> Int -> m ()
 {-# INLINE unsafeSwap #-}
 unsafeSwap = G.unsafeSwap
 
+-- | Replace the element at the given position and return the old element. No
+-- bounds checks are performed.
+unsafeExchange :: (PrimMonad m, Unbox a) => MVector (PrimState m) a -> Int -> a -> m a
+{-# INLINE unsafeExchange #-}
+unsafeExchange = G.unsafeExchange
+
 -- Filling and copying
 -- -------------------
 
@@ -348,6 +397,156 @@
 nextPermutation :: (PrimMonad m,Ord e,Unbox e) => MVector (PrimState m) e -> m Bool
 {-# INLINE nextPermutation #-}
 nextPermutation = G.nextPermutation
+
+
+-- Folds
+-- -----
+
+-- | /O(n)/ Apply the monadic action to every element of the vector, discarding the results.
+--
+-- @since 0.12.3.0
+mapM_ :: (PrimMonad m, Unbox a) => (a -> m b) -> MVector (PrimState m) a -> m ()
+{-# INLINE mapM_ #-}
+mapM_ = G.mapM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector and its index,
+-- discarding the results.
+--
+-- @since 0.12.3.0
+imapM_ :: (PrimMonad m, Unbox a) => (Int -> a -> m b) -> MVector (PrimState m) a -> m ()
+{-# INLINE imapM_ #-}
+imapM_ = G.imapM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector,
+-- discarding the results. It's same as the @flip mapM_@.
+--
+-- @since 0.12.3.0
+forM_ :: (PrimMonad m, Unbox a) => MVector (PrimState m) a -> (a -> m b) -> m ()
+{-# INLINE forM_ #-}
+forM_ = G.forM_
+
+-- | /O(n)/ Apply the monadic action to every element of the vector
+-- and its index, discarding the results. It's same as the @flip imapM_@.
+--
+-- @since 0.12.3.0
+iforM_ :: (PrimMonad m, Unbox a) => MVector (PrimState m) a -> (Int -> a -> m b) -> m ()
+{-# INLINE iforM_ #-}
+iforM_ = G.iforM_
+
+-- | /O(n)/ Pure left fold.
+--
+-- @since 0.12.3.0
+foldl :: (PrimMonad m, Unbox a) => (b -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldl #-}
+foldl = G.foldl
+
+-- | /O(n)/ Pure left fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldl' :: (PrimMonad m, Unbox a) => (b -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldl' #-}
+foldl' = G.foldl'
+
+-- | /O(n)/ Pure left fold (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldl :: (PrimMonad m, Unbox a) => (b -> Int -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldl #-}
+ifoldl = G.ifoldl
+
+-- | /O(n)/ Pure left fold with strict accumulator (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldl' :: (PrimMonad m, Unbox a) => (b -> Int -> a -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldl' #-}
+ifoldl' = G.ifoldl'
+
+-- | /O(n)/ Pure right fold.
+--
+-- @since 0.12.3.0
+foldr :: (PrimMonad m, Unbox a) => (a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldr #-}
+foldr = G.foldr
+
+-- | /O(n)/ Pure right fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldr' :: (PrimMonad m, Unbox a) => (a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldr' #-}
+foldr' = G.foldr'
+
+-- | /O(n)/ Pure right fold (function applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldr :: (PrimMonad m, Unbox a) => (Int -> a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldr #-}
+ifoldr = G.ifoldr
+
+-- | /O(n)/ Pure right fold with strict accumulator (function applied
+-- to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldr' :: (PrimMonad m, Unbox a) => (Int -> a -> b -> b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldr' #-}
+ifoldr' = G.ifoldr'
+
+-- | /O(n)/ Monadic fold.
+--
+-- @since 0.12.3.0
+foldM :: (PrimMonad m, Unbox a) => (b -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldM #-}
+foldM = G.foldM
+
+-- | /O(n)/ Monadic fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldM' :: (PrimMonad m, Unbox a) => (b -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldM' #-}
+foldM' = G.foldM'
+
+-- | /O(n)/ Monadic fold (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldM :: (PrimMonad m, Unbox a) => (b -> Int -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldM #-}
+ifoldM = G.ifoldM
+
+-- | /O(n)/ Monadic fold with strict accumulator (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldM' :: (PrimMonad m, Unbox a) => (b -> Int -> a -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldM' #-}
+ifoldM' = G.ifoldM'
+
+-- | /O(n)/ Monadic right fold.
+--
+-- @since 0.12.3.0
+foldrM :: (PrimMonad m, Unbox a) => (a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldrM #-}
+foldrM = G.foldrM
+
+-- | /O(n)/ Monadic right fold with strict accumulator.
+--
+-- @since 0.12.3.0
+foldrM' :: (PrimMonad m, Unbox a) => (a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE foldrM' #-}
+foldrM' = G.foldrM'
+
+-- | /O(n)/ Monadic right fold (action applied to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldrM :: (PrimMonad m, Unbox a) => (Int -> a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldrM #-}
+ifoldrM = G.ifoldrM
+
+-- | /O(n)/ Monadic right fold with strict accumulator (action applied
+-- to each element and its index).
+--
+-- @since 0.12.3.0
+ifoldrM' :: (PrimMonad m, Unbox a) => (Int -> a -> b -> m b) -> b -> MVector (PrimState m) a -> m b
+{-# INLINE ifoldrM' #-}
+ifoldrM' = G.ifoldrM'
+
 
 #define DEFINE_MUTABLE
 #include "unbox-tuple-instances"
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,15 @@
+# Changes in version 0.12.3.0
+
+ * Fix performance regression due to introduction of `keepAlive#` primop in ghc-9.0: [#372](https://github.com/haskell/vector/pull/372)
+
+ * Add monadic functions for mutable vectors: [#338](https://github.com/haskell/vector/pull/338)
+
+   * Added folds for monadic functions: `mapM_`, `imapM_`, `forM_`, `iforM_`,
+     `foldl`, `foldl'`, `foldM`, `foldM'`, `ifoldl`, `ifoldl'`, `ifoldM`,
+     `ifoldM'`
+   * Added `modifyM` and `unsafeModifyM` for mutable vectors
+   * Added `generate` and `generateM` for mutable vectors
+
 # Changes in version 0.12.2.0
 
  * Add `MINIMAL` pragma to `Vector` & `MVector` type classes: [#11](https://github.com/haskell/vector/issues/11)
diff --git a/tests/Tests/Vector/Property.hs b/tests/Tests/Vector/Property.hs
--- a/tests/Tests/Vector/Property.hs
+++ b/tests/Tests/Vector/Property.hs
@@ -28,12 +28,14 @@
 import Utilities as Util hiding (limitUnfolds)
 
 import Control.Monad
-import Data.Functor.Identity
+import Control.Monad.ST
 import qualified Data.Traversable as T (Traversable(..))
 import Data.Foldable (Foldable(foldMap))
+import Data.Functor.Identity
 import Data.Orphans ()
-
+import Data.Foldable (foldrM)
 import qualified Data.Vector.Generic as V
+import qualified Data.Vector.Generic.Mutable as MV
 import qualified Data.Vector.Fusion.Bundle as S
 
 import Test.QuickCheck
@@ -196,7 +198,17 @@
         'prop_prescanr, 'prop_prescanr',
         'prop_postscanr, 'prop_postscanr',
         'prop_scanr, 'prop_scanr', 'prop_scanr1, 'prop_scanr1',
-        'prop_iscanr, 'prop_iscanr'
+        'prop_iscanr, 'prop_iscanr',
+
+        -- Mutable API
+        'prop_mut_read, 'prop_mut_write, 'prop_mut_modify,
+
+        'prop_mut_generate, 'prop_mut_generateM,
+        'prop_mut_mapM_, 'prop_mut_imapM_, 'prop_mut_forM_, 'prop_mut_iforM_,
+        'prop_mut_foldr, 'prop_mut_foldr', 'prop_mut_foldl, 'prop_mut_foldl',
+        'prop_mut_ifoldr, 'prop_mut_ifoldr', 'prop_mut_ifoldl, 'prop_mut_ifoldl',
+        'prop_mut_foldM, 'prop_mut_foldM', 'prop_mut_foldrM, 'prop_mut_foldrM',
+        'prop_mut_ifoldM, 'prop_mut_ifoldM', 'prop_mut_ifoldrM, 'prop_mut_ifoldrM'
     ])
   where
     -- Prelude
@@ -473,6 +485,110 @@
 
         constructrN xs 0 _ = xs
         constructrN xs n f = constructrN (f xs : xs) (n-1) f
+
+    prop_mut_foldr :: P ((a -> a -> a) -> a -> v a -> a) =
+      (\f z v -> runST $ MV.foldr f z =<< V.thaw v) `eq` foldr
+    prop_mut_foldr' :: P ((a -> a -> a) -> a -> v a -> a) =
+      (\f z v -> runST $ MV.foldr' f z =<< V.thaw v) `eq` foldr
+    prop_mut_foldl :: P ((a -> a -> a) -> a -> v a -> a) =
+      (\f z v -> runST $ MV.foldl f z =<< V.thaw v) `eq` foldl
+    prop_mut_foldl' :: P ((a -> a -> a) -> a -> v a -> a) =
+      (\f z v -> runST $ MV.foldl' f z =<< V.thaw v) `eq` foldl'
+    prop_mut_ifoldr :: P ((Int -> a -> a -> a) -> a -> v a -> a) =
+      (\f z v -> runST $ MV.ifoldr f z =<< V.thaw v) `eq` ifoldr
+    prop_mut_ifoldr' :: P ((Int -> a -> a -> a) -> a -> v a -> a) =
+      (\f z v -> runST $ MV.ifoldr' f z =<< V.thaw v) `eq` ifoldr
+    prop_mut_ifoldl :: P ((a -> Int -> a -> a) -> a -> v a -> a) =
+      (\f z v -> runST $ MV.ifoldl f z =<< V.thaw v) `eq` ifoldl
+    prop_mut_ifoldl' :: P ((a -> Int -> a -> a) -> a -> v a -> a) =
+      (\f z v -> runST $ MV.ifoldl' f z =<< V.thaw v) `eq` ifoldl
+
+    prop_mut_foldM :: P ((a -> a -> Identity a) -> a -> v a -> Identity a)
+      = (\f z v -> Identity $ runST $ MV.foldM (\b -> pure . runIdentity . f b) z =<< V.thaw v)
+      `eq` foldM
+    prop_mut_foldM' :: P ((a -> a -> Identity a) -> a -> v a -> Identity a)
+      = (\f z v -> Identity $ runST $ MV.foldM' (\b -> pure . runIdentity . f b) z =<< V.thaw v)
+      `eq` foldM
+    prop_mut_foldrM :: P ((a -> a -> Identity a) -> a -> v a -> Identity a)
+      = (\f z v -> Identity $ runST $ MV.foldrM (\a -> pure . runIdentity . f a) z =<< V.thaw v)
+      `eq`
+      foldrM
+    prop_mut_foldrM' :: P ((a -> a -> Identity a) -> a -> v a -> Identity a)
+      = (\f z v -> Identity $ runST $ MV.foldrM' (\a b -> pure $ runIdentity $ f a b) z =<< V.thaw v)
+      `eq`
+      foldrM
+
+    prop_mut_read = \xs ->
+      not (V.null xs) ==>
+      forAll (choose (0, V.length xs-1)) $ \i ->
+      unP prop xs i
+      where
+        prop :: P (v a -> Int -> a) = (\v i -> runST $ do mv <- V.thaw v
+                                                          MV.read mv i
+                                      ) `eq` (!!)
+    prop_mut_write = \xs ->
+      not (V.null xs) ==>
+      forAll (choose (0, V.length xs-1)) $ \i ->
+      unP prop xs i
+      where
+        prop :: P (v a -> Int -> a -> v a) = (\v i a -> runST $ do mv <- V.thaw v
+                                                                   MV.write mv i a
+                                                                   V.freeze mv
+                                             ) `eq` writeList
+    prop_mut_modify = \xs f ->
+      not (V.null xs) ==>
+      forAll (choose (0, V.length xs-1)) $ \i ->
+      unP prop xs f i
+      where
+        prop :: P (v a -> (a -> a) -> Int -> v a)
+          = (\v f i -> runST $ do mv <- V.thaw v
+                                  MV.modify mv f i
+                                  V.freeze mv
+            ) `eq` modifyList
+
+
+
+    prop_mut_generate :: P (Int -> (Int -> a) -> v a)
+      = (\n _ -> n < 1000) ===> (\n f -> runST $ V.freeze =<< MV.generate n f)
+      `eq` Util.generate
+    prop_mut_generateM :: P (Int -> (Int -> Writer [a] a) -> Writer [a] (v a))
+      = (\n _ -> n < 1000) ===> (\n f -> liftRunST $ V.freeze =<< MV.generateM n (hoistST . f))
+      `eq` Util.generateM
+
+    prop_mut_ifoldM :: P ((a -> Int -> a -> Identity a) -> a -> v a -> Identity a)
+      = (\f z v -> Identity $ runST $ MV.ifoldM (\b i -> pure . runIdentity . f b i) z =<< V.thaw v)
+      `eq` ifoldM
+    prop_mut_ifoldM' :: P ((a -> Int -> a -> Identity a) -> a -> v a -> Identity a)
+      = (\f z v -> Identity $ runST $ MV.ifoldM' (\b i -> pure . runIdentity . f b i) z =<< V.thaw v)
+      `eq` ifoldM
+    prop_mut_ifoldrM :: P ((Int -> a -> a -> Identity a) -> a -> v a -> Identity a)
+      = (\f z v -> Identity $ runST $ MV.ifoldrM (\i b -> pure . runIdentity . f i b) z =<< V.thaw v)
+      `eq`
+      ifoldrM
+    prop_mut_ifoldrM' :: P ((Int -> a -> a -> Identity a) -> a -> v a -> Identity a)
+      = (\f z v -> Identity $ runST $ MV.ifoldrM' (\i b -> pure . runIdentity . f i b) z =<< V.thaw v)
+      `eq`
+      ifoldrM
+
+    prop_mut_forM_ :: P (v a -> (a -> Writer [a] ()) -> Writer [a] ())
+      = (\v f -> liftRunST $ do mv <- V.thaw v
+                                MV.forM_ mv (hoistST . f))
+      `eq` flip mapM_
+    prop_mut_iforM_ :: P (v a -> (Int -> a -> Writer [a] ()) -> Writer [a] ())
+      = (\v f -> liftRunST $ do mv <- V.thaw v
+                                MV.iforM_ mv (\i x -> hoistST $ f i x))
+      `eq` flip imapM_
+    prop_mut_mapM_ :: P ((a -> Writer [a] ()) -> v a -> Writer [a] ())
+      = (\f v -> liftRunST $ MV.mapM_ (hoistST . f) =<< V.thaw v) `eq` mapM_
+    prop_mut_imapM_ :: P ((Int -> a -> Writer [a] ()) -> v a -> Writer [a] ())
+      = (\f v -> liftRunST $ MV.imapM_ (\i x -> hoistST $ f i x) =<< V.thaw v) `eq` imapM_
+
+
+liftRunST :: (forall s. WriterT w (ST s) a) -> Writer w a
+liftRunST m = WriterT $ Identity $ runST $ runWriterT m
+
+hoistST :: Writer w a -> WriterT w (ST s) a
+hoistST = WriterT . pure . runWriter
 
 -- copied from GHC source code
 partitionWith :: (a -> Either b c) -> [a] -> ([b], [c])
diff --git a/tests/Utilities.hs b/tests/Utilities.hs
--- a/tests/Utilities.hs
+++ b/tests/Utilities.hs
@@ -3,6 +3,7 @@
 
 import Test.QuickCheck
 
+import Data.Foldable
 import qualified Data.Vector as DV
 import qualified Data.Vector.Generic as DVG
 import qualified Data.Vector.Primitive as DVP
@@ -278,6 +279,15 @@
 
 withIndexFirst m f = m (uncurry f) . zip [0..]
 
+modifyList :: [a] -> (a -> a) -> Int -> [a]
+modifyList xs f i = zipWith merge xs (replicate i Nothing ++ [Just f] ++ repeat Nothing)
+  where
+    merge x Nothing  = x
+    merge x (Just g) = g x
+
+writeList :: [a] -> Int -> a -> [a]
+writeList xs i a = modifyList xs (const a) i
+
 imap :: (Int -> a -> a) -> [a] -> [a]
 imap = withIndexFirst map
 
@@ -322,8 +332,11 @@
 ifoldr :: (Int -> a -> b -> b) -> b -> [a] -> b
 ifoldr f z = foldr (uncurry f) z . zip [0..]
 
-ifoldM :: Monad m => (a -> Int -> a -> m a) -> a -> [a] -> m a
+ifoldM :: Monad m => (b -> Int -> a -> m b) -> b -> [a] -> m b
 ifoldM = indexedLeftFold foldM
+
+ifoldrM :: Monad m => (Int -> a -> b -> m b) -> b -> [a] -> m b
+ifoldrM f z xs = foldrM (\(i,a) b -> f i a b) z ([0..] `zip` xs)
 
 ifoldM_ :: Monad m => (b -> Int -> a -> m b) -> b -> [a] -> m ()
 ifoldM_ = indexedLeftFold foldM_
diff --git a/vector.cabal b/vector.cabal
--- a/vector.cabal
+++ b/vector.cabal
@@ -1,5 +1,5 @@
 Name:           vector
-Version:        0.12.2.0
+Version:        0.12.3.0
 -- don't forget to update the changelog file!
 License:        BSD3
 License-File:   LICENSE