diff --git a/saw/SAWScript/REPL/Command.hs b/saw/SAWScript/REPL/Command.hs
index c5cbdd9ed2..227de3f641 100644
--- a/saw/SAWScript/REPL/Command.hs
+++ b/saw/SAWScript/REPL/Command.hs
@@ -228,9 +228,8 @@ sawScriptCmd str = do
     Left err -> io $ print err
     Right stmt ->
       do ro <- getTopLevelRO
-         ie <- getEnvironment
-         ((), ie') <- io $ runTopLevel (interpretStmt True stmt) ro ie
-         putEnvironment ie'
+         rwRef <- getEnvironmentRef
+         io $ runTopLevel (interpretStmt True stmt) ro rwRef
 
 replFileName :: String
 replFileName = "<stdin>"
diff --git a/saw/SAWScript/REPL/Monad.hs b/saw/SAWScript/REPL/Monad.hs
index b2e6d02ba8..6d24cde547 100644
--- a/saw/SAWScript/REPL/Monad.hs
+++ b/saw/SAWScript/REPL/Monad.hs
@@ -38,12 +38,12 @@ module SAWScript.REPL.Monad (
   , getTermEnv, modifyTermEnv, setTermEnv
   , getExtraTypes, modifyExtraTypes, setExtraTypes
   , getExtraNames, modifyExtraNames, setExtraNames
-  , getRW
 
     -- ** SAWScript stuff
   , getSharedContext
   , getTopLevelRO
   , getEnvironment, modifyEnvironment, putEnvironment
+  , getEnvironmentRef
   , getSAWScriptNames
   ) where
 
@@ -96,50 +96,53 @@ deriving instance Typeable AIG.Proxy
 
 -- REPL Environment ------------------------------------------------------------
 
--- REPL RW Environment.
-data RW = RW
-  { eContinue   :: Bool
-  , eIsBatch    :: Bool
-  , eTopLevelRO :: TopLevelRO
-  , environment :: TopLevelRW
+-- REPL Environment.
+data Refs = Refs
+  { eContinue   :: IORef Bool
+  , eIsBatch    :: IORef Bool
+  , eTopLevelRO :: IORef TopLevelRO
+  , environment :: IORef TopLevelRW
   }
 
 -- | Initial, empty environment.
-defaultRW :: Bool -> Options -> IO RW
-defaultRW isBatch opts = do
+defaultRefs :: Bool -> Options -> IO Refs
+defaultRefs isBatch opts =
 #ifdef USE_BUILTIN_ABC
-  (_biContext, ro, rw) <- buildTopLevelEnv (AIGProxy GIA.proxy) opts
+  do (_biContext, ro, rw) <- buildTopLevelEnv (AIGProxy GIA.proxy) opts
 #else
-  (_biContext, ro, rw) <- buildTopLevelEnv (AIGProxy AIG.basicProxy) opts
+  do (_biContext, ro, rw) <- buildTopLevelEnv (AIGProxy AIG.basicProxy) opts
 #endif
-
-  return RW
-    { eContinue   = True
-    , eIsBatch    = isBatch
-    , eTopLevelRO = ro
-    , environment = rw
-    }
+     contRef <- newIORef True
+     batchRef <- newIORef isBatch
+     roRef <- newIORef ro
+     rwRef <- newIORef rw
+     return Refs
+       { eContinue   = contRef
+       , eIsBatch    = batchRef
+       , eTopLevelRO = roRef
+       , environment = rwRef
+       }
 
 -- | Build up the prompt for the REPL.
-mkPrompt :: RW -> String
-mkPrompt rw
-  | eIsBatch rw = ""
-  | otherwise   = "sawscript> "
+mkPrompt :: Bool {- ^ is batch -} -> String
+mkPrompt batch
+  | batch     = ""
+  | otherwise = "sawscript> "
 
-mkTitle :: RW -> String
-mkTitle _rw = "sawscript"
+mkTitle :: Refs -> String
+mkTitle _refs = "sawscript"
 
 
 -- REPL Monad ------------------------------------------------------------------
 
 -- | REPL_ context with InputT handling.
-newtype REPL a = REPL { unREPL :: IORef RW -> IO a }
+newtype REPL a = REPL { unREPL :: Refs -> IO a }
 
 -- | Run a REPL action with a fresh environment.
 runREPL :: Bool -> Options -> REPL a -> IO a
-runREPL isBatch opts m = do
-  ref <- newIORef =<< defaultRW isBatch opts
-  unREPL m ref
+runREPL isBatch opts m =
+  do refs <- defaultRefs isBatch opts
+     unREPL m refs
 
 instance Functor REPL where
   {-# INLINE fmap #-}
@@ -247,31 +250,35 @@ rethrowEvalError m = run `X.catch` rethrow
 io :: IO a -> REPL a
 io m = REPL (\ _ -> m)
 
-getRW :: REPL RW
-getRW  = REPL readIORef
+getRefs :: REPL Refs
+getRefs = REPL pure
+
+readRef :: (Refs -> IORef a) -> REPL a
+readRef r = REPL (\refs -> readIORef (r refs))
 
-modifyRW_ :: (RW -> RW) -> REPL ()
-modifyRW_ f = REPL (\ ref -> modifyIORef ref f)
+modifyRef :: (Refs -> IORef a) -> (a -> a) -> REPL ()
+modifyRef r f = REPL (\refs -> modifyIORef (r refs) f)
 
 -- | Construct the prompt for the current environment.
 getPrompt :: REPL String
-getPrompt  = mkPrompt `fmap` getRW
+getPrompt = mkPrompt <$> readRef eIsBatch
 
 shouldContinue :: REPL Bool
-shouldContinue  = eContinue `fmap` getRW
+shouldContinue = readRef eContinue
 
 stop :: REPL ()
-stop  = modifyRW_ (\ rw -> rw { eContinue = False })
+stop = modifyRef eContinue (const False)
 
 unlessBatch :: REPL () -> REPL ()
-unlessBatch body = do
-  rw <- getRW
-  unless (eIsBatch rw) body
+unlessBatch body =
+  do batch <- readRef eIsBatch
+     unless batch body
 
 setREPLTitle :: REPL ()
-setREPLTitle  = unlessBatch $ do
-  rw <- getRW
-  io (setTitle (mkTitle rw))
+setREPLTitle =
+  unlessBatch $
+  do refs <- getRefs
+     io (setTitle (mkTitle refs))
 
 getVars :: REPL (Map.Map T.Name M.IfaceDecl)
 getVars  = do
@@ -361,17 +368,19 @@ getSharedContext :: REPL SharedContext
 getSharedContext = fmap roSharedContext getTopLevelRO
 
 getTopLevelRO :: REPL TopLevelRO
-getTopLevelRO = fmap eTopLevelRO getRW
+getTopLevelRO = readRef eTopLevelRO
+
+getEnvironmentRef :: REPL (IORef TopLevelRW)
+getEnvironmentRef = environment <$> getRefs
 
 getEnvironment :: REPL TopLevelRW
-getEnvironment = fmap environment getRW
+getEnvironment = readRef environment
 
 putEnvironment :: TopLevelRW -> REPL ()
 putEnvironment = modifyEnvironment . const
 
 modifyEnvironment :: (TopLevelRW -> TopLevelRW) -> REPL ()
-modifyEnvironment f = modifyRW_ $ \current ->
-  current { environment = f (environment current) }
+modifyEnvironment = modifyRef environment
 
 -- | Get visible variable names for Haskeline completion.
 getSAWScriptNames :: REPL [String]
diff --git a/src/SAWScript/Builtins.hs b/src/SAWScript/Builtins.hs
index ac265ec643..6acbbebf59 100644
--- a/src/SAWScript/Builtins.hs
+++ b/src/SAWScript/Builtins.hs
@@ -34,6 +34,7 @@ import qualified Data.ByteString as StrictBS
 import qualified Data.ByteString.Lazy as BS
 import qualified Data.ByteString.Lazy.UTF8 as B
 import qualified Data.IntMap as IntMap
+import Data.IORef
 import Data.List (isPrefixOf, isInfixOf)
 import qualified Data.Map as Map
 import Data.Set (Set)
@@ -1147,7 +1148,8 @@ failsPrim :: TopLevel SV.Value -> TopLevel ()
 failsPrim m = do
   topRO <- getTopLevelRO
   topRW <- getTopLevelRW
-  x <- liftIO $ Ex.try (runTopLevel m topRO topRW)
+  ref <- liftIO $ newIORef topRW
+  x <- liftIO $ Ex.try (runTopLevel m topRO ref)
   case x of
     Left (ex :: Ex.SomeException) ->
       do liftIO $ putStrLn "== Anticipated failure message =="
diff --git a/src/SAWScript/Interpreter.hs b/src/SAWScript/Interpreter.hs
index 7f631b5a25..f2ddc27088 100644
--- a/src/SAWScript/Interpreter.hs
+++ b/src/SAWScript/Interpreter.hs
@@ -38,6 +38,7 @@ import Control.Monad (unless, (>=>), when)
 import Control.Monad.IO.Class (liftIO)
 import qualified Data.ByteString as BS
 import Data.Foldable (foldrM)
+import Data.IORef
 import qualified Data.Map as Map
 import Data.Map ( Map )
 import qualified Data.Set as Set
@@ -277,7 +278,9 @@ interpretStmts env stmts =
              interpretStmts env' ss
 
 stmtInterpreter :: StmtInterpreter
-stmtInterpreter ro rw stmts = fmap fst $ runTopLevel (interpretStmts emptyLocal stmts) ro rw
+stmtInterpreter ro rw stmts =
+  do ref <- newIORef rw
+     runTopLevel (interpretStmts emptyLocal stmts) ro ref
 
 processStmtBind :: Bool -> SS.Pattern -> Maybe SS.Type -> SS.Expr -> TopLevel ()
 processStmtBind printBinds pat _mc expr = do -- mx mt
@@ -490,7 +493,8 @@ processFile proxy opts file = do
   oldpath <- getCurrentDirectory
   file' <- canonicalizePath file
   setCurrentDirectory (takeDirectory file')
-  _ <- runTopLevel (interpretFile file' True) ro rw
+  ref <- newIORef rw
+  _ <- runTopLevel (interpretFile file' True) ro ref
             `X.catch` (handleException opts)
   setCurrentDirectory oldpath
   return ()
diff --git a/src/SAWScript/Value.hs b/src/SAWScript/Value.hs
index bb4f1bfd7d..a756639f86 100644
--- a/src/SAWScript/Value.hs
+++ b/src/SAWScript/Value.hs
@@ -436,12 +436,9 @@ instance Wrapped (TopLevel a) where
 instance MonadFail TopLevel where
   fail = throwTopLevel
 
-runTopLevel :: TopLevel a -> TopLevelRO -> TopLevelRW -> IO (a, TopLevelRW)
-runTopLevel (TopLevel m) ro rw =
-  do ref <- newIORef rw
-     x <- runReaderT (runReaderT m ro) ref
-     rw' <- readIORef ref
-     pure (x, rw')
+runTopLevel :: TopLevel a -> TopLevelRO -> IORef TopLevelRW -> IO a
+runTopLevel (TopLevel m) ro ref =
+  runReaderT (runReaderT m ro) ref
 
 io :: IO a -> TopLevel a
 io f = liftIO f