Use a Deque

yesod-core/yesod-core.cabal

@@ -46,7 +46,7 @@ library
                    , path-pieces           >= 0.1.2    && < 0.3
                    , random                >= 1.0.0.2  && < 1.2
                    , resourcet             >= 1.2
-                   , rio
+                   , rio                   >= 0.1.9
                    , rio-orphans
                    , shakespeare           >= 2.0
                    , template-haskell      >= 2.11

yesod-form/Yesod/Form/Fields.hs

@@ -765,7 +765,7 @@ fileAFormReq :: RenderMessage site FormMessage
 fileAFormReq fs = AForm $ do
     site <- getYesod
     langs <- reqLangs <$> getRequest
-    WFormData viewsRef mfd <- view id
+    WFormData viewsDeque mfd <- view id
     ints <- readIORef $ mfdInts mfd
     let (name, ints') =
             case fsName fs of
@@ -796,14 +796,14 @@ $newline never
             , fvRequired = True
             }
     writeIORef (mfdEnctype mfd) Multipart
-    modifyIORef viewsRef $ \views -> views . (fv:)
+    pushBackDeque viewsDeque fv
     return res
 
 fileAFormOpt :: FieldSettings site -> AForm site (Maybe FileInfo)
 fileAFormOpt fs = AForm $ do
     master <- getYesod
     langs <- reqLangs <$> getRequest
-    WFormData viewsRef mfd <- view id
+    WFormData viewsDeque mfd <- view id
     ints <- readIORef $ mfdInts mfd
     let (name, ints') =
             case fsName fs of
@@ -832,7 +832,7 @@ $newline never
             , fvRequired = False
             }
     writeIORef (mfdEnctype mfd) Multipart
-    modifyIORef viewsRef $ \views -> views . (fv:)
+    pushBackDeque viewsDeque fv
     return res
 
 incrInts :: Ints -> Ints

yesod-form/Yesod/Form/Functions.hs

@@ -107,9 +107,9 @@ newFormIdent = do
 
 formToAForm :: MForm site (FormResult a, [FieldView site]) -> AForm site a
 formToAForm mform = AForm $ do
-  WFormData viewsRef mfd <- view id
+  WFormData viewsDeque mfd <- view id
   (a, views) <- runRIO mfd mform
-  modifyIORef' viewsRef $ \front -> front . (views++)
+  for_ views $ pushBackDeque viewsDeque
   pure a
 
 aFormToForm :: AForm site a
@@ -162,11 +162,11 @@ wFormToMForm
   :: WForm site a                      -- ^ input form
   -> MForm site (a, [FieldView site])  -- ^ output form
 wFormToMForm wform = do
-  viewsRef <- newIORef id
+  viewsDeque <- newDeque
   mfd <- view id
-  a <- runRIO (WFormData viewsRef mfd) wform
-  views <- readIORef viewsRef
-  pure (a, views [])
+  a <- runRIO (WFormData viewsDeque mfd) wform
+  views <- dequeToList viewsDeque
+  pure (a, views)
 
 -- | Converts a monadic form 'MForm' into another monadic form 'WForm'.
 --
@@ -175,9 +175,9 @@ mFormToWForm
   :: MForm site (a, FieldView site)  -- ^ input form
   -> WForm site a                    -- ^ output form
 mFormToWForm mform = do
-  WFormData views mfd <- view id
+  WFormData viewsDeque mfd <- view id
   (a, view') <- runRIO mfd mform
-  modifyIORef' views $ \front -> front . (view':)
+  pushBackDeque viewsDeque view'
   pure a
 
 -- | Converts a form field into monadic form. This field requires a value

yesod-form/Yesod/Form/Types.hs

@@ -145,7 +145,7 @@ type FileEnv = Map.Map Text [FileInfo]
 -- @since 1.4.14
 type WForm site = RIO (WFormData site)
 data WFormData site = WFormData
-  { wfdViews :: !(IORef ([FieldView site] -> [FieldView site]))
+  { wfdViews :: !(BDeque (PrimState IO) (FieldView site))
   , wfdMfd :: !(MFormData site)
   }
 instance HasHandlerData (WFormData site) where