require strings to be non-empty

frontend/app/Form/Input.hs

@@ -10,18 +10,26 @@ import Miso.String (fromMisoString, toMisoString)
 
 input :: String -> Form T.Text T.Text
 input label =
-  Form
+  let parse :: T.Text -> Either String T.Text
+      parse i =
+        let i' = T.strip i
+         in if T.null i' then Left "required" else Right i'
+   in Form
         { view = \i ->
             [ div_ [] $
                 [ label_ [] $
                     [ text (toMisoString label),
-                  input_
+                      div_ [] $
+                        [ input_
                             [ type_ "text",
                               value_ (toMisoString i),
                               onInput fromMisoString
+                            ],
+                          div_ [] $
+                            [either (text . toMisoString) (\_ -> text "") (parse i)]
                         ]
                     ]
                 ]
             ],
-      fill = \i -> Right i
+          fill = parse
         }