Accumulate button result correctly

src/Handler/Utils/Form.hs

@@ -15,6 +15,8 @@ import qualified Data.Map as Map
 import Handler.Utils.DateTime
 import Data.String (IsString(..))
 
+import qualified Data.Foldable as Foldable
+
 -- import Yesod.Core
 import qualified Data.Text as T
 -- import Yesod.Form.Types
@@ -53,17 +55,19 @@ buttonForm html = do
   buttonIdent <- newFormIdent
   resultWidgetMap <- forM buttonMap $ \val -> mopt (button val) ("" { fsName = Just buttonIdent }) Nothing
     
-  let result = asum $ nothing2miss <$> fst <$> Map.elems resultWidgetMap
+  let result = accResult $ fst <$> Map.elems resultWidgetMap
   let viewF = (Map.!) (snd <$> resultWidgetMap)
   
   return (result, viewF)
+  where
+    accResult :: Foldable f => f (FormResult (Maybe a)) -> FormResult a
+    accResult = Foldable.foldr accResult' FormMissing
 
-nothing2miss :: FormResult (Maybe a) -> FormResult a
+    accResult' :: FormResult (Maybe a) -> FormResult a -> FormResult a
-nothing2miss (FormSuccess Nothing)  = FormMissing
+    accResult' (FormSuccess _) (FormSuccess _) = FormFailure ["Ambiguous parse"]
-nothing2miss (FormSuccess (Just r)) = FormSuccess r
+    accResult' (FormSuccess (Just x)) _ = FormSuccess x
-nothing2miss (FormFailure msgs)     = FormFailure msgs
+    accResult' (FormFailure errs) _ = FormFailure errs
-nothing2miss (FormMissing)          = FormMissing
+    accResult' _ x = x
-  
   
 ----------------------------
 -- Buttons (old version ) --