diff --git a/.github/workflows/haskell.yaml b/.github/workflows/haskell.yaml
index 2656d83..9683c00 100644
--- a/.github/workflows/haskell.yaml
+++ b/.github/workflows/haskell.yaml
@@ -10,12 +10,19 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ghc: ['8.4', '8.6', '8.8', '8.10', '9.0', '9.2', '9.4', '9.6']
+        ghc: ['8.4', '8.6', '8.8', '8.10', '9.0', '9.2', '9.4', '9.6', '9.8']
     steps:
-      - uses: actions/checkout@v3
-      - uses: haskell/actions/setup@v2
+      - uses: actions/checkout@v4
+      - uses: haskell-actions/setup@v2
+        id: setup-haskell
         with:
           ghc-version: ${{ matrix.ghc }}
+      - uses: actions/cache@v3
+        with:
+          path: |
+            ${{ steps.setup-haskell.outputs.cabal-store }}
+            dist-newstyle
+          key: ${{ runner.os }}-${{ matrix.ghc }}
       - name: Build
         run: cabal build
       - name: Test
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a238138..01d77d2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+# 0.2.1.0 - December 2023
+
+* Add `findIndexL`, `findIndexR`, `findIndicesL`, `findIndicesR`
+* Fix bug in `|>` & `<|` ([#10](https://github.com/konsumlamm/rrb-vector/issues/10))
+
 # 0.2.0.1 - October 2023
 
 * Support `primitive-0.9` and `deepseq-1.5`
diff --git a/rrb-vector-strict.cabal b/rrb-vector-strict.cabal
index 614fdb8..212a9db 100644
--- a/rrb-vector-strict.cabal
+++ b/rrb-vector-strict.cabal
@@ -1,5 +1,5 @@
 name:               rrb-vector-strict
-version:            0.2.0.1
+version:            0.2.1.0
 synopsis:           Efficient RRB-Vectors
 description:
   An RRB-Vector is an efficient sequence data structure.
@@ -31,8 +31,9 @@ tested-with:
   GHC == 8.10.7
   GHC == 9.0.2
   GHC == 9.2.8
-  GHC == 9.4.7
+  GHC == 9.4.8
   GHC == 9.6.3
+  GHC == 9.8.1
 
 source-repository head
   type:     git
@@ -61,7 +62,7 @@ test-suite test
     Strictness
   type:                 exitcode-stdio-1.0
   ghc-options:          -Wall -Wno-orphans -Wno-type-defaults
-  build-depends:        base, deepseq, quickcheck-classes-base, rrb-vector-strict, tasty, tasty-quickcheck
+  build-depends:        base, containers, deepseq, quickcheck-classes-base, rrb-vector, tasty, tasty-quickcheck
   if impl(ghc >= 8.6)
     build-depends:      nothunks
   default-language:     Haskell2010
diff --git a/src/Data/RRBVector/Strict.hs b/src/Data/RRBVector/Strict.hs
index 917f011..8ab9e4c 100644
--- a/src/Data/RRBVector/Strict.hs
+++ b/src/Data/RRBVector/Strict.hs
@@ -33,6 +33,7 @@ module Data.RRBVector.Strict
     , adjust, adjust'
     , take, drop, splitAt
     , insertAt, deleteAt
+    , findIndexL, findIndexR, findIndicesL, findIndicesR
     -- * With Index
     --
     -- | Reexported from [indexed-traversable](https://hackage.haskell.org/package/indexed-traversable).
diff --git a/src/Data/RRBVector/Strict/Internal.hs b/src/Data/RRBVector/Strict/Internal.hs
index e96267a..977fddd 100644
--- a/src/Data/RRBVector/Strict/Internal.hs
+++ b/src/Data/RRBVector/Strict/Internal.hs
@@ -24,6 +24,7 @@ module Data.RRBVector.Strict.Internal
     , adjust, adjust'
     , take, drop, splitAt
     , insertAt, deleteAt
+    , findIndexL, findIndexR, findIndicesL, findIndicesR
     -- * Transformations
     , map, map', reverse
     -- * Zipping and unzipping
@@ -651,6 +652,22 @@ insertAt i x v = let (left, right) = splitAt i v in (left |> x) >< right
 deleteAt :: Int -> Vector a -> Vector a
 deleteAt i v = let (left, right) = splitAt (i + 1) v in take i left >< right
 
+-- | \(O(n)\). Find the first index from the left that satisfies the predicate.
+findIndexL :: (a -> Bool) -> Vector a -> Maybe Int
+findIndexL f = ifoldr (\i x acc -> if f x then Just i else acc) Nothing
+
+-- | \(O(n)\). Find the first index from the right that satisfies the predicate.
+findIndexR :: (a -> Bool) -> Vector a -> Maybe Int
+findIndexR f = ifoldl (\i acc x -> if f x then Just i else acc) Nothing
+
+-- | \(O(n)\). Find the indices that satisfy the predicate, starting from the left.
+findIndicesL :: (a -> Bool) -> Vector a -> [Int]
+findIndicesL f = ifoldr (\i x acc -> if f x then i : acc else acc) []
+
+-- | \(O(n)\). Find the indices that satisfy the predicate, starting from the right.
+findIndicesR :: (a -> Bool) -> Vector a -> [Int]
+findIndicesR f = ifoldl (\i acc x -> if f x then i : acc else acc) []
+
 -- concatenation
 
 -- | \(O(\log \max(n_1, n_2))\). Concatenates two vectors.
diff --git a/test/Properties.hs b/test/Properties.hs
index 62d188a..c283465 100644
--- a/test/Properties.hs
+++ b/test/Properties.hs
@@ -1,5 +1,7 @@
 {-# LANGUAGE CPP #-}
 
+{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
+
 module Properties
     ( properties
     ) where
@@ -12,6 +14,7 @@ import Data.List (uncons)
 import Data.Proxy (Proxy(..))
 import Prelude hiding ((==)) -- use @===@ instead
 
+import qualified Data.Sequence as Seq
 import qualified Data.RRBVector.Strict as V
 import Test.QuickCheck.Classes.Base
 import Test.Tasty
@@ -135,6 +138,22 @@ properties = testGroup "properties"
         , testProperty "satisfies `deleteAt 0 v = drop 1 v`" $ \v -> V.deleteAt 0 v === V.drop 1 v
         , testProperty "satisfies `deleteAt (length v - 1) v = take (length v - 1) v`" $ \v -> V.deleteAt (length v - 1) v === V.take (length v - 1) v
         ]
+    , testGroup "findIndexL"
+        [ testProperty "finds the first index" $ \v (Fn f) -> V.findIndexL f v === Seq.findIndexL f (Seq.fromList (toList v))
+        , testProperty "returns Nothing for the empty vector" $ \(Fn f) -> V.findIndexL f V.empty === Nothing
+        ]
+    , testGroup "findIndexR"
+        [ testProperty "finds the last index" $ \v (Fn f) -> V.findIndexR f v === Seq.findIndexR f (Seq.fromList (toList v))
+        , testProperty "returns Nothing for the empty vector" $ \(Fn f) -> V.findIndexR f V.empty === Nothing
+        ]
+    , localOption (QuickCheckMaxSize 1000) $ testGroup "findIndicesL"
+        [ testProperty "finds the indices starting from the left" $ \v (Fn f) -> V.findIndicesL f v === Seq.findIndicesL f (Seq.fromList (toList v))
+        , testProperty "returns [] for the empty vector" $ \(Fn f) -> V.findIndicesL f V.empty === []
+        ]
+    , localOption (QuickCheckMaxSize 1000) $ testGroup "findIndicesR"
+        [ testProperty "finds the indices starting from the right" $ \v (Fn f) -> V.findIndicesR f v === Seq.findIndicesR f (Seq.fromList (toList v))
+        , testProperty "returns [] for the empty vector" $ \(Fn f) -> V.findIndicesR f V.empty === []
+        ]
     , testGroup "reverse"
         [ testProperty "reverses the vector" $ \v -> toList (V.reverse v) === reverse (toList v)
         ]