diff --git a/.github/workflows/haskell.yml b/.github/workflows/haskell.yml
index ff64d1e42..ce6dd1d9f 100644
--- a/.github/workflows/haskell.yml
+++ b/.github/workflows/haskell.yml
@@ -18,7 +18,7 @@ jobs:
 
     - uses: haskell/actions/setup@v1
       with:
-        ghc-version: '8.10'
+        ghc-version: '9.2.1'
         cabal-version: '3.6'
 
     - name: Cache
diff --git a/builder/src/Deps/Solver.hs b/builder/src/Deps/Solver.hs
index 59fb9d683..2b90ee449 100644
--- a/builder/src/Deps/Solver.hs
+++ b/builder/src/Deps/Solver.hs
@@ -278,9 +278,6 @@ instance Applicative Solver where
        in solverFunc state okF back err
 
 instance Monad Solver where
-  return a =
-    Solver $ \state ok back _ -> ok state a back
-
   (>>=) (Solver solverA) callback =
     Solver $ \state ok back err ->
       let okA stateA a backA =
diff --git a/compiler/src/Data/Name.hs b/compiler/src/Data/Name.hs
index b1500e4a3..5f65bdb8b 100644
--- a/compiler/src/Data/Name.hs
+++ b/compiler/src/Data/Name.hs
@@ -233,7 +233,7 @@ fromTypeVariable name@(Utf8.Utf8 ba#) index =
     else
       let len# = sizeofByteArray# ba#
           end# = indexWord8Array# ba# (len# -# 1#)
-       in if isTrue# (leWord# 0x30## end#) && isTrue# (leWord# end# 0x39##)
+       in if isTrue# (leWord8# (wordToWord8# 0x30##) end#) && isTrue# (leWord8# end# (wordToWord8# 0x39##))
             then
               runST
                 ( do
@@ -298,11 +298,11 @@ fromManyNames names =
             ( ST $ \s ->
                 case newByteArray# (len# +# 3#) s of
                   (# s, mba# #) ->
-                    case writeWord8Array# mba# 0# 0x5F## {-_-} s of
+                    case writeWord8Array# mba# 0# (wordToWord8# 0x5F## {-_-}) s of
                       s ->
-                        case writeWord8Array# mba# 1# 0x4D## {-M-} s of
+                        case writeWord8Array# mba# 1# (wordToWord8# 0x4D## {-M-}) s of
                           s ->
-                            case writeWord8Array# mba# 2# 0x24## s of
+                            case writeWord8Array# mba# 2# (wordToWord8# 0x24##) s of
                               s ->
                                 case copyByteArray# ba# 0# mba# 3# len# s of
                                   s ->
diff --git a/compiler/src/Data/Utf8.hs b/compiler/src/Data/Utf8.hs
index a3ec14311..1c9c85435 100644
--- a/compiler/src/Data/Utf8.hs
+++ b/compiler/src/Data/Utf8.hs
@@ -90,11 +90,11 @@ contains :: Word8 -> Utf8 t -> Bool
 contains (W8# word#) (Utf8 ba#) =
   containsHelp word# ba# 0# (sizeofByteArray# ba#)
 
-containsHelp :: Word# -> ByteArray# -> Int# -> Int# -> Bool
+containsHelp :: Word8# -> ByteArray# -> Int# -> Int# -> Bool
 containsHelp word# ba# !offset# len# =
   if isTrue# (offset# <# len#)
     then
-      if isTrue# (eqWord# word# (indexWord8Array# ba# offset#))
+      if isTrue# (eqWord8# word# (indexWord8Array# ba# offset#))
         then True
         else containsHelp word# ba# (offset# +# 1#) len#
     else False
@@ -116,7 +116,7 @@ startsWithChar isGood bytes@(Utf8 ba#) =
   if isEmpty bytes
     then False
     else
-      let !w# = indexWord8Array# ba# 0#
+      let !w# = indexWord8ArrayAsWord# ba# 0#
           !char
             | isTrue# (ltWord# w# 0xC0##) = C# (chr# (word2Int# w#))
             | isTrue# (ltWord# w# 0xE0##) = chr2 ba# 0# w#
@@ -130,7 +130,7 @@ endsWithWord8 :: Word8 -> Utf8 t -> Bool
 endsWithWord8 (W8# w#) (Utf8 ba#) =
   let len# = sizeofByteArray# ba#
    in isTrue# (len# ># 0#)
-        && isTrue# (eqWord# w# (indexWord8Array# ba# (len# -# 1#)))
+        && isTrue# (eqWord8# w# (indexWord8Array# ba# (len# -# 1#)))
 
 -- SPLIT
 
@@ -146,12 +146,12 @@ splitHelp str start offsets =
     offset : offsets ->
       unsafeSlice str start offset : splitHelp str (offset + 1) offsets
 
-findDividers :: Word# -> ByteArray# -> Int# -> Int# -> [Int] -> [Int]
+findDividers :: Word8# -> ByteArray# -> Int# -> Int# -> [Int] -> [Int]
 findDividers divider# ba# !offset# len# revOffsets =
   if isTrue# (offset# <# len#)
     then
       findDividers divider# ba# (offset# +# 1#) len# $
-        if isTrue# (eqWord# divider# (indexWord8Array# ba# offset#))
+        if isTrue# (eqWord8# divider# (indexWord8Array# ba# offset#))
           then I# offset# : revOffsets
           else revOffsets
     else reverse revOffsets
@@ -286,7 +286,7 @@ toCharsHelp ba# offset# len# =
   if isTrue# (offset# >=# len#)
     then []
     else
-      let !w# = indexWord8Array# ba# offset#
+      let !w# = indexWord8ArrayAsWord# ba# offset#
           !(# char, width# #)
             | isTrue# (ltWord# w# 0xC0##) = (# C# (chr# (word2Int# w#)), 1# #)
             | isTrue# (ltWord# w# 0xE0##) = (# chr2 ba# offset# w#, 2# #)
@@ -300,7 +300,7 @@ toCharsHelp ba# offset# len# =
 chr2 :: ByteArray# -> Int# -> Word# -> Char
 chr2 ba# offset# firstWord# =
   let !i1# = word2Int# firstWord#
-      !i2# = word2Int# (indexWord8Array# ba# (offset# +# 1#))
+      !i2# = word2Int# (indexWord8ArrayAsWord# ba# (offset# +# 1#))
       !c1# = uncheckedIShiftL# (i1# -# 0xC0#) 6#
       !c2# = i2# -# 0x80#
    in C# (chr# (c1# +# c2#))
@@ -309,8 +309,8 @@ chr2 ba# offset# firstWord# =
 chr3 :: ByteArray# -> Int# -> Word# -> Char
 chr3 ba# offset# firstWord# =
   let !i1# = word2Int# firstWord#
-      !i2# = word2Int# (indexWord8Array# ba# (offset# +# 1#))
-      !i3# = word2Int# (indexWord8Array# ba# (offset# +# 2#))
+      !i2# = word2Int# (indexWord8ArrayAsWord# ba# (offset# +# 1#))
+      !i3# = word2Int# (indexWord8ArrayAsWord# ba# (offset# +# 2#))
       !c1# = uncheckedIShiftL# (i1# -# 0xE0#) 12#
       !c2# = uncheckedIShiftL# (i2# -# 0x80#) 6#
       !c3# = i3# -# 0x80#
@@ -320,9 +320,9 @@ chr3 ba# offset# firstWord# =
 chr4 :: ByteArray# -> Int# -> Word# -> Char
 chr4 ba# offset# firstWord# =
   let !i1# = word2Int# firstWord#
-      !i2# = word2Int# (indexWord8Array# ba# (offset# +# 1#))
-      !i3# = word2Int# (indexWord8Array# ba# (offset# +# 2#))
-      !i4# = word2Int# (indexWord8Array# ba# (offset# +# 3#))
+      !i2# = word2Int# (indexWord8ArrayAsWord# ba# (offset# +# 1#))
+      !i3# = word2Int# (indexWord8ArrayAsWord# ba# (offset# +# 2#))
+      !i4# = word2Int# (indexWord8ArrayAsWord# ba# (offset# +# 3#))
       !c1# = uncheckedIShiftL# (i1# -# 0xF0#) 18#
       !c2# = uncheckedIShiftL# (i2# -# 0x80#) 12#
       !c3# = uncheckedIShiftL# (i3# -# 0x80#) 6#
@@ -386,7 +386,7 @@ escape :: Word8 -> Word8 -> Ptr a -> Utf8 t -> Int -> Int -> Int -> IO ()
 escape before@(W8# before#) after ptr name@(Utf8 ba#) offset@(I# offset#) len@(I# len#) i@(I# i#) =
   if isTrue# (i# <# len#)
     then
-      if isTrue# (eqWord# before# (indexWord8Array# ba# (offset# +# i#)))
+      if isTrue# (eqWord8# before# (indexWord8Array# ba# (offset# +# i#)))
         then do
           writeWordToPtr ptr i after
           escape before after ptr name offset len (i + 1)
diff --git a/compiler/src/Elm/Compiler/Type.hs b/compiler/src/Elm/Compiler/Type.hs
index 395c093bf..9dfbab192 100644
--- a/compiler/src/Elm/Compiler/Type.hs
+++ b/compiler/src/Elm/Compiler/Type.hs
@@ -1,5 +1,5 @@
 {-# LANGUAGE OverloadedStrings #-}
-{-# OPTIONS_GHC -Wall #-}
+{-# OPTIONS_GHC -Wall -Wno-incomplete-uni-patterns #-}
 
 module Elm.Compiler.Type
   ( Type (..),
diff --git a/compiler/src/Json/Decode.hs b/compiler/src/Json/Decode.hs
index 8aad424ed..008283c73 100644
--- a/compiler/src/Json/Decode.hs
+++ b/compiler/src/Json/Decode.hs
@@ -100,7 +100,9 @@ instance Functor (Decoder x) where
 
 instance Applicative (Decoder x) where
   {-# INLINE pure #-}
-  pure = return
+  pure a =
+    Decoder $ \_ ok _ ->
+      ok a
 
   {-# INLINE (<*>) #-}
   (<*>) (Decoder decodeFunc) (Decoder decodeArg) =
@@ -111,11 +113,6 @@ instance Applicative (Decoder x) where
        in decodeFunc ast okF err
 
 instance Monad (Decoder x) where
-  {-# INLINE return #-}
-  return a =
-    Decoder $ \_ ok _ ->
-      ok a
-
   {-# INLINE (>>=) #-}
   (>>=) (Decoder decodeA) callback =
     Decoder $ \ast ok err ->
diff --git a/compiler/src/Parse/Primitives.hs b/compiler/src/Parse/Primitives.hs
index 2280c8bc3..c3e5e24ea 100644
--- a/compiler/src/Parse/Primitives.hs
+++ b/compiler/src/Parse/Primitives.hs
@@ -82,7 +82,9 @@ instance Functor (Parser x) where
 
 instance Applicative.Applicative (Parser x) where
   {-# INLINE pure #-}
-  pure = return
+  pure value =
+    Parser $ \state _ eok _ _ ->
+      eok value state
 
   {-# INLINE (<*>) #-}
   (<*>) (Parser parserFunc) (Parser parserArg) =
@@ -152,11 +154,6 @@ oowfHelp state cok eok cerr parsers fallback =
 -- MONAD
 
 instance Monad (Parser x) where
-  {-# INLINE return #-}
-  return value =
-    Parser $ \state _ eok _ _ ->
-      eok value state
-
   {-# INLINE (>>=) #-}
   (Parser parserA) >>= callback =
     Parser $ \state cok eok cerr eerr ->
diff --git a/compiler/src/Parse/Variable.hs b/compiler/src/Parse/Variable.hs
index 266cd181d..ea0a78929 100644
--- a/compiler/src/Parse/Variable.hs
+++ b/compiler/src/Parse/Variable.hs
@@ -25,7 +25,7 @@ import qualified Data.Name as Name
 import qualified Data.Set as Set
 import Data.Word (Word8)
 import Foreign.Ptr (Ptr, plusPtr)
-import GHC.Exts (Char (C#), Int#, chr#, uncheckedIShiftL#, word2Int#, (+#), (-#))
+import GHC.Exts (Char (C#), Int#, chr#, uncheckedIShiftL#, word2Int#, word8ToWord#, (+#), (-#))
 import GHC.Word (Word8 (W8#))
 import Parse.Primitives (Col, Parser, Row, unsafeIndex)
 import qualified Parse.Primitives as P
@@ -305,4 +305,4 @@ chr4 pos firstWord =
 
 unpack :: Word8 -> Int#
 unpack (W8# word#) =
-  word2Int# word#
+  word2Int# (word8ToWord# word#)
diff --git a/compiler/src/Reporting/Render/Code.hs b/compiler/src/Reporting/Render/Code.hs
index cc645af9b..0bf5aab1f 100644
--- a/compiler/src/Reporting/Render/Code.hs
+++ b/compiler/src/Reporting/Render/Code.hs
@@ -18,6 +18,7 @@ import qualified Data.ByteString.UTF8 as UTF8_BS
 import qualified Data.Char as Char
 import qualified Data.IntSet as IntSet
 import qualified Data.List as List
+import qualified Data.Maybe as Maybe
 import qualified Data.Name as Name
 import qualified Data.Set as Set
 import Data.Word (Word16)
@@ -146,7 +147,7 @@ renderPair source@(Source sourceLines) region1 region2 =
               spaces2 = replicate (fromIntegral (startCol2 - endCol1)) ' '
               zigzag2 = replicate (fromIntegral (endCol2 - startCol2)) '^'
 
-              (Just line) = List.lookup startRow1 sourceLines
+              line = Maybe.fromJust $ List.lookup startRow1 sourceLines
            in OneLine $
                 D.vcat
                   [ D.fromChars lineNumber <> "| " <> D.fromChars line,
diff --git a/compiler/src/Reporting/Result.hs b/compiler/src/Reporting/Result.hs
index 694791c49..85bbf4d23 100644
--- a/compiler/src/Reporting/Result.hs
+++ b/compiler/src/Reporting/Result.hs
@@ -83,20 +83,16 @@ instance Applicative (Result i w e) where
              in kv i1 w1 bad2 good2
        in kf i w bad1 good1
 
-instance Monad (Result i w e) where
-  return = ok
+  (*>) (Result ka) (Result kb) =
+    Result $ \i w bad good ->
+      let good1 i1 w1 _ =
+            kb i1 w1 bad good
+       in ka i w bad good1
 
+instance Monad (Result i w e) where
   (>>=) (Result ka) callback =
     Result $ \i w bad good ->
       let good1 i1 w1 a =
             case callback a of
               Result kb -> kb i1 w1 bad good
        in ka i w bad good1
-
-  (>>) (Result ka) (Result kb) =
-    Result $ \i w bad good ->
-      let good1 i1 w1 _ =
-            kb i1 w1 bad good
-       in ka i w bad good1
-
--- PERF add INLINE to these?
diff --git a/compiler/src/Type/Unify.hs b/compiler/src/Type/Unify.hs
index 249d88f10..95d8c934e 100644
--- a/compiler/src/Type/Unify.hs
+++ b/compiler/src/Type/Unify.hs
@@ -73,11 +73,12 @@ instance Applicative Unify where
              in kv vars1 ok2 err
        in kf vars ok1 err
 
-instance Monad Unify where
-  return a =
-    Unify $ \vars ok _ ->
-      ok vars a
+  (*>) (Unify ka) (Unify kb) =
+    Unify $ \vars ok err ->
+      let ok1 vars1 _ = kb vars1 ok err
+       in ka vars ok1 err
 
+instance Monad Unify where
   (>>=) (Unify ka) callback =
     Unify $ \vars ok err ->
       let ok1 vars1 a =
@@ -85,11 +86,6 @@ instance Monad Unify where
               Unify kb -> kb vars1 ok err
        in ka vars ok1 err
 
-  (>>) (Unify ka) (Unify kb) =
-    Unify $ \vars ok err ->
-      let ok1 vars1 _ = kb vars1 ok err
-       in ka vars ok1 err
-
 register :: IO Variable -> Unify Variable
 register mkVar =
   Unify $ \vars ok _ ->
diff --git a/gren.cabal b/gren.cabal
index b0697707a..1fa970fd7 100644
--- a/gren.cabal
+++ b/gren.cabal
@@ -193,9 +193,9 @@ Executable gren
     Build-depends:
         ansi-terminal >= 0.11 && < 0.12,
         ansi-wl-pprint >= 0.6.8 && < 0.7,
-        base >=4.11 && <5,
+        base >=4.16 && <5,
         binary >= 0.8 && < 0.9,
-        bytestring >= 0.10 && < 0.11,
+        bytestring >= 0.11 && < 0.12,
         containers >= 0.6 && < 0.7,
         directory >= 1.2.3.0 && < 2.0,
         edit-distance >= 0.2 && < 0.3,
diff --git a/terminal/src/Repl.hs b/terminal/src/Repl.hs
index 61916e07b..1b325521f 100644
--- a/terminal/src/Repl.hs
+++ b/terminal/src/Repl.hs
@@ -31,6 +31,7 @@ import qualified Data.ByteString.UTF8 as BS_UTF8
 import qualified Data.Char as Char
 import qualified Data.List as List
 import qualified Data.Map as Map
+import qualified Data.Maybe as Maybe
 import qualified Data.Name as N
 import qualified Directories as Dirs
 import qualified Elm.Constraint as C
@@ -423,8 +424,9 @@ attemptEval (Env root interpreter ansi) oldState newState output =
 interpret :: FilePath -> B.Builder -> IO Exit.ExitCode
 interpret interpreter javascript =
   let createProcess = (Proc.proc interpreter []) {Proc.std_in = Proc.CreatePipe}
-   in Proc.withCreateProcess createProcess $ \(Just stdin) _ _ handle ->
+   in Proc.withCreateProcess createProcess $ \maybeStdIn _ _ handle ->
         do
+          let stdin = Maybe.fromJust maybeStdIn
           B.hPutBuilder stdin javascript
           IO.hClose stdin
           Proc.waitForProcess handle