support optional fields

frontend/app/Page/EditValue.hs

@@ -10,6 +10,7 @@ where
 import Api
 import Data.Aeson qualified as A
 import Data.Aeson.KeyMap qualified as AM
+import Data.ByteString.Lazy.UTF8 as LB
 import Data.Maybe
 import Form qualified as F
 import Miso
@@ -52,7 +53,8 @@ viewModel m = do
   let input = (fromMaybe (A.Object AM.empty) m.input)
   div_ [] $
     [ viewForm input m.schema,
-      viewInput input
+      viewInput input,
+      viewOutput input m.schema
     ]
 
 viewForm :: A.Value -> Schema -> View Action
@@ -64,3 +66,13 @@ viewForm input =
 viewInput :: A.Value -> View Action
 viewInput input =
   pre_ [] [text (toMisoString (A.encode input))]
+
+viewOutput :: A.Value -> Schema -> View Action
+viewOutput input schema =
+  pre_ [] $
+    [ text $
+        toMisoString
+          ( either ("Left " <>) (("Right " <>) . LB.toString) $
+              (A.encode <$> ((schemaForm schema).fill input))
+          )
+    ]