diff --git a/MsgSpec.md b/MsgSpec.md
--- a/MsgSpec.md
+++ b/MsgSpec.md
@@ -8,26 +8,17 @@
 ## Creating widgets
 
 Let's say the user types in some code, and the only effect of that code is the creation of a widget.
-The kernel will open a comm for the widget, and store a reference to that comm inside it. Then, to
-notify the frontend about the creation of a widget, an initial state update is sent on the widget's
-comm.
+The kernel will open a comm for the widget, and store a reference to that comm. The comm_open message
+also holds the initial state of the widget in it, which is used by the frontend to create a model for
+the widget.
 
 > The comm should be opened with a `target_name` of `"ipython.widget"`.
 
-The initial state update message looks like this:
-
-```json
-{
-    "method": "update",
-    "state": { "<some/all widget properties>" }
-}
-```
-
 Any *numeric* property initialized with the empty string is provided the default value by the
-frontend. Some numbers need to be sent as actual numbers (when non-null), whereas some (especially
-those used by sliders) need to be sent as strings.
+frontend. Some numbers need to be sent as actual numbers (when non-null), whereas the ones representing
+lengths in CSS units need to be sent as strings.
 
-The initial state update must *at least* have the following fields:
+The initial state must *at least* have the following fields:
 
   - `msg_throttle` (default 3): To prevent the kernel from flooding with messages, the messages from
     the widget to the kernel are throttled. If `msg_throttle` messages were sent, and all are still
@@ -43,8 +34,8 @@
 
   - Rest of the properties as required initially.
 
-This state update is also used with fragments of the overall state to sync changes between the
-frontend and the kernel.
+This state is also used with fragments of the overall state to sync changes between the frontend and
+the kernel.
 
 ## Displaying widgets
 
@@ -111,7 +102,7 @@
 input widget, when an `input_request` is received.
 
 Now, widgets cannot send `execute_request` messages. They can only send `comm_data` messages, which
-means that it's not possible to fetch input through widget events.
+means that it's not possible to fetch input inside widget event handlers.
 
 ---
 
diff --git a/ihaskell-widgets.cabal b/ihaskell-widgets.cabal
--- a/ihaskell-widgets.cabal
+++ b/ihaskell-widgets.cabal
@@ -10,7 +10,7 @@
 -- PVP summary:      +-+------- breaking API changes
 --                   | | +----- non-breaking API additions
 --                   | | | +--- code changes with no API change
-version:             0.2.2.0
+version:             0.2.2.1
 
 -- A short (one-line) description of the package.
 synopsis:            IPython standard widgets for IHaskell.
@@ -104,7 +104,7 @@
                      , nats -any
                      , vinyl >= 0.5
                      , vector -any
-                     , singletons >= 0.9.0
+                     , singletons >= 0.9.0 && <2.0.0.0
                      , scientific -any
                      , unix -any
 
diff --git a/src/IHaskell/Display/Widgets.hs b/src/IHaskell/Display/Widgets.hs
--- a/src/IHaskell/Display/Widgets.hs
+++ b/src/IHaskell/Display/Widgets.hs
@@ -41,7 +41,6 @@
 import           IHaskell.Display.Widgets.String.TextArea as X
 
 import           IHaskell.Display.Widgets.Common as X
-import           IHaskell.Display.Widgets.Types as X (setField, getField, properties,
-                                                      triggerDisplay, triggerChange, triggerClick,
-                                                      triggerSelection, triggerSubmit,
-                                                      ChildWidget(..))
+import           IHaskell.Display.Widgets.Types as X (setField, getField, properties, triggerDisplay,
+                                                      triggerChange, triggerClick, triggerSelection,
+                                                      triggerSubmit, ChildWidget(..))
diff --git a/src/IHaskell/Display/Widgets/Bool/CheckBox.hs b/src/IHaskell/Display/Widgets/Bool/CheckBox.hs
--- a/src/IHaskell/Display/Widgets/Bool/CheckBox.hs
+++ b/src/IHaskell/Display/Widgets/Bool/CheckBox.hs
@@ -12,12 +12,10 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
 import           Data.Aeson
 import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
 import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/Bool/ToggleButton.hs b/src/IHaskell/Display/Widgets/Bool/ToggleButton.hs
--- a/src/IHaskell/Display/Widgets/Bool/ToggleButton.hs
+++ b/src/IHaskell/Display/Widgets/Bool/ToggleButton.hs
@@ -12,7 +12,6 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
 import           Data.Aeson
 import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
diff --git a/src/IHaskell/Display/Widgets/Bool/Valid.hs b/src/IHaskell/Display/Widgets/Bool/Valid.hs
--- a/src/IHaskell/Display/Widgets/Bool/Valid.hs
+++ b/src/IHaskell/Display/Widgets/Bool/Valid.hs
@@ -4,19 +4,16 @@
 {-# LANGUAGE TypeSynonymInstances #-}
 
 module IHaskell.Display.Widgets.Bool.Valid (
-  -- * The Valid Widget
-  ValidWidget,
-  -- * Constructor
-  mkValidWidget) where
+-- * The Valid Widget
+ValidWidget, 
+             -- * Constructor
+             mkValidWidget) where
 
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
 import           Data.Aeson
-import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
-import           Data.Text (Text)
 import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
diff --git a/src/IHaskell/Display/Widgets/Box/Box.hs b/src/IHaskell/Display/Widgets/Box/Box.hs
--- a/src/IHaskell/Display/Widgets/Box/Box.hs
+++ b/src/IHaskell/Display/Widgets/Box/Box.hs
@@ -12,19 +12,14 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
-import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
-import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
 import           IHaskell.IPython.Message.UUID as U
 
 import           IHaskell.Display.Widgets.Types
-import           IHaskell.Display.Widgets.Common
 
 -- | A 'Box' represents a Box widget from IPython.html.widgets.
 type Box = IPythonWidget BoxType
diff --git a/src/IHaskell/Display/Widgets/Box/FlexBox.hs b/src/IHaskell/Display/Widgets/Box/FlexBox.hs
--- a/src/IHaskell/Display/Widgets/Box/FlexBox.hs
+++ b/src/IHaskell/Display/Widgets/Box/FlexBox.hs
@@ -12,11 +12,8 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
-import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
-import           Data.Text (Text)
 import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
diff --git a/src/IHaskell/Display/Widgets/Box/PlaceProxy.hs b/src/IHaskell/Display/Widgets/Box/PlaceProxy.hs
--- a/src/IHaskell/Display/Widgets/Box/PlaceProxy.hs
+++ b/src/IHaskell/Display/Widgets/Box/PlaceProxy.hs
@@ -3,21 +3,17 @@
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE TypeSynonymInstances #-}
 
-
 module IHaskell.Display.Widgets.Box.PlaceProxy (
-  -- * The PlaceProxy widget
-  PlaceProxy,
-  -- * Constructor
-  mkPlaceProxy) where
+-- * The PlaceProxy widget
+PlaceProxy, 
+            -- * Constructor
+            mkPlaceProxy) where
 
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
-import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
-import           Data.Text (Text)
 import           Data.Vinyl (Rec(..), (<+>))
 import           Data.Vinyl.Lens (rput)
 
diff --git a/src/IHaskell/Display/Widgets/Box/Proxy.hs b/src/IHaskell/Display/Widgets/Box/Proxy.hs
--- a/src/IHaskell/Display/Widgets/Box/Proxy.hs
+++ b/src/IHaskell/Display/Widgets/Box/Proxy.hs
@@ -5,18 +5,15 @@
 
 module IHaskell.Display.Widgets.Box.Proxy (
 -- * The Proxy widget
-ProxyWidget,
-     -- * Constructor
-     mkProxyWidget) where
+ProxyWidget, 
+             -- * Constructor
+             mkProxyWidget) where
 
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
-import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
-import           Data.Text (Text)
 import           Data.Vinyl (Rec(..), (<+>))
 import           Data.Vinyl.Lens (rput)
 
diff --git a/src/IHaskell/Display/Widgets/Box/SelectionContainer/Accordion.hs b/src/IHaskell/Display/Widgets/Box/SelectionContainer/Accordion.hs
--- a/src/IHaskell/Display/Widgets/Box/SelectionContainer/Accordion.hs
+++ b/src/IHaskell/Display/Widgets/Box/SelectionContainer/Accordion.hs
@@ -12,13 +12,11 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
 import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
 import qualified Data.Scientific as Sci
 import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/Box/SelectionContainer/Tab.hs b/src/IHaskell/Display/Widgets/Box/SelectionContainer/Tab.hs
--- a/src/IHaskell/Display/Widgets/Box/SelectionContainer/Tab.hs
+++ b/src/IHaskell/Display/Widgets/Box/SelectionContainer/Tab.hs
@@ -12,13 +12,11 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
 import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
 import qualified Data.Scientific as Sci
 import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/Button.hs b/src/IHaskell/Display/Widgets/Button.hs
--- a/src/IHaskell/Display/Widgets/Button.hs
+++ b/src/IHaskell/Display/Widgets/Button.hs
@@ -12,7 +12,7 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
+import           Control.Monad (when)
 import           Data.Aeson
 import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
diff --git a/src/IHaskell/Display/Widgets/Common.hs b/src/IHaskell/Display/Widgets/Common.hs
--- a/src/IHaskell/Display/Widgets/Common.hs
+++ b/src/IHaskell/Display/Widgets/Common.hs
@@ -4,12 +4,15 @@
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE GADTs #-}
+{-# LANGUAGE AutoDeriveTypeable #-}
+{-# LANGUAGE DeriveDataTypeable #-}
 
 module IHaskell.Display.Widgets.Common where
 
 import           Data.Aeson
 import           Data.Aeson.Types (emptyObject)
 import           Data.Text (pack, Text)
+import           Data.Typeable (Typeable)
 
 import           IHaskell.Display (IHaskellWidget)
 import           IHaskell.Eval.Widgets (widgetSendClose)
@@ -97,11 +100,11 @@
 closeWidget :: IHaskellWidget w => w -> IO ()
 closeWidget w = widgetSendClose w emptyObject
 
-newtype StrInt = StrInt Integer
-  deriving (Num, Ord, Eq, Enum)
+newtype PixCount = PixCount Integer
+  deriving (Num, Ord, Eq, Enum, Typeable)
 
-instance ToJSON StrInt where
-  toJSON (StrInt x) = toJSON . pack $ show x
+instance ToJSON PixCount where
+  toJSON (PixCount x) = toJSON . pack $ show x ++ "px"
 
 -- | Pre-defined border styles
 data BorderStyleValue = NoBorder
@@ -201,7 +204,7 @@
 data ImageFormatValue = PNG
                       | SVG
                       | JPG
-  deriving Eq
+  deriving (Eq, Typeable)
 
 instance Show ImageFormatValue where
   show PNG = "png"
diff --git a/src/IHaskell/Display/Widgets/Float/BoundedFloat/BoundedFloatText.hs b/src/IHaskell/Display/Widgets/Float/BoundedFloat/BoundedFloatText.hs
--- a/src/IHaskell/Display/Widgets/Float/BoundedFloat/BoundedFloatText.hs
+++ b/src/IHaskell/Display/Widgets/Float/BoundedFloat/BoundedFloatText.hs
@@ -13,13 +13,11 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
 import qualified Data.Scientific as Sci
 import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/Float/BoundedFloat/FloatProgress.hs b/src/IHaskell/Display/Widgets/Float/BoundedFloat/FloatProgress.hs
--- a/src/IHaskell/Display/Widgets/Float/BoundedFloat/FloatProgress.hs
+++ b/src/IHaskell/Display/Widgets/Float/BoundedFloat/FloatProgress.hs
@@ -12,13 +12,8 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Exception (throw, ArithException(LossOfPrecision))
-import           Control.Monad (when, join)
 import           Data.Aeson
-import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
-import qualified Data.Scientific as Sci
-import           Data.Text (Text)
 import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
diff --git a/src/IHaskell/Display/Widgets/Float/BoundedFloat/FloatSlider.hs b/src/IHaskell/Display/Widgets/Float/BoundedFloat/FloatSlider.hs
--- a/src/IHaskell/Display/Widgets/Float/BoundedFloat/FloatSlider.hs
+++ b/src/IHaskell/Display/Widgets/Float/BoundedFloat/FloatSlider.hs
@@ -12,7 +12,6 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
diff --git a/src/IHaskell/Display/Widgets/Float/BoundedFloatRange/FloatRangeSlider.hs b/src/IHaskell/Display/Widgets/Float/BoundedFloatRange/FloatRangeSlider.hs
--- a/src/IHaskell/Display/Widgets/Float/BoundedFloatRange/FloatRangeSlider.hs
+++ b/src/IHaskell/Display/Widgets/Float/BoundedFloatRange/FloatRangeSlider.hs
@@ -13,8 +13,6 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Exception (throw, ArithException(LossOfPrecision))
-import           Control.Monad (when, join, void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
diff --git a/src/IHaskell/Display/Widgets/Float/FloatText.hs b/src/IHaskell/Display/Widgets/Float/FloatText.hs
--- a/src/IHaskell/Display/Widgets/Float/FloatText.hs
+++ b/src/IHaskell/Display/Widgets/Float/FloatText.hs
@@ -12,13 +12,11 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
 import qualified Data.Scientific as Sci
 import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/Image.hs b/src/IHaskell/Display/Widgets/Image.hs
--- a/src/IHaskell/Display/Widgets/Image.hs
+++ b/src/IHaskell/Display/Widgets/Image.hs
@@ -12,12 +12,9 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
-import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
 import           Data.Monoid (mempty)
-import           Data.Text (Text)
 import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
diff --git a/src/IHaskell/Display/Widgets/Int/BoundedInt/BoundedIntText.hs b/src/IHaskell/Display/Widgets/Int/BoundedInt/BoundedIntText.hs
--- a/src/IHaskell/Display/Widgets/Int/BoundedInt/BoundedIntText.hs
+++ b/src/IHaskell/Display/Widgets/Int/BoundedInt/BoundedIntText.hs
@@ -12,13 +12,11 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
 import qualified Data.Scientific as Sci
 import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/Int/BoundedInt/IntProgress.hs b/src/IHaskell/Display/Widgets/Int/BoundedInt/IntProgress.hs
--- a/src/IHaskell/Display/Widgets/Int/BoundedInt/IntProgress.hs
+++ b/src/IHaskell/Display/Widgets/Int/BoundedInt/IntProgress.hs
@@ -12,13 +12,8 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Exception (throw, ArithException(LossOfPrecision))
-import           Control.Monad (when, join)
 import           Data.Aeson
-import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
-import qualified Data.Scientific as Sci
-import           Data.Text (Text)
 import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
diff --git a/src/IHaskell/Display/Widgets/Int/BoundedInt/IntSlider.hs b/src/IHaskell/Display/Widgets/Int/BoundedInt/IntSlider.hs
--- a/src/IHaskell/Display/Widgets/Int/BoundedInt/IntSlider.hs
+++ b/src/IHaskell/Display/Widgets/Int/BoundedInt/IntSlider.hs
@@ -12,7 +12,6 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
diff --git a/src/IHaskell/Display/Widgets/Int/BoundedIntRange/IntRangeSlider.hs b/src/IHaskell/Display/Widgets/Int/BoundedIntRange/IntRangeSlider.hs
--- a/src/IHaskell/Display/Widgets/Int/BoundedIntRange/IntRangeSlider.hs
+++ b/src/IHaskell/Display/Widgets/Int/BoundedIntRange/IntRangeSlider.hs
@@ -12,7 +12,6 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
diff --git a/src/IHaskell/Display/Widgets/Int/IntText.hs b/src/IHaskell/Display/Widgets/Int/IntText.hs
--- a/src/IHaskell/Display/Widgets/Int/IntText.hs
+++ b/src/IHaskell/Display/Widgets/Int/IntText.hs
@@ -12,13 +12,11 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
 import qualified Data.Scientific as Sci
 import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/Interactive.hs b/src/IHaskell/Display/Widgets/Interactive.hs
--- a/src/IHaskell/Display/Widgets/Interactive.hs
+++ b/src/IHaskell/Display/Widgets/Interactive.hs
@@ -1,14 +1,11 @@
-{-# LANGUAGE DataKinds #-}
 {-# LANGUAGE TypeFamilies #-}
-{-# LANGUAGE ConstraintKinds #-}
-{-# LANGUAGE UndecidableInstances #-}
-{-# LANGUAGE GADTs #-}
+{-# LANGUAGE DataKinds #-}
 {-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE GADTs #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE PolyKinds #-}
-{-# LANGUAGE KindSignatures #-}
-{-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE PatternSynonyms #-}
 
 module IHaskell.Display.Widgets.Interactive (interactive, uncurryHList, Rec(..), Argument(..)) where
 
@@ -25,7 +22,7 @@
 
 import           IHaskell.Display.Widgets.Types
 import           IHaskell.Display.Widgets.Common
-import qualified IHaskell.Display.Widgets.Singletons as S (SField(..), Field(..))
+import qualified IHaskell.Display.Widgets.Singletons as S (SField, Field(..))
 
 import           IHaskell.Display.Widgets.Box.FlexBox
 import           IHaskell.Display.Widgets.Bool.CheckBox
@@ -44,10 +41,6 @@
               a
               -> WidgetConf a
 
-newtype WrappedConstructor a =
-          WrappedConstructor
-            { wrappedConstructor :: IO (IPythonWidget (SuitableWidget a)) }
-
  
 type family WithTypes (ts :: [*]) (r :: *) :: * where
         WithTypes '[] r = r
@@ -70,8 +63,6 @@
 
 newtype Initializer a = Initializer (IPythonWidget (SuitableWidget a) -> Argument a -> IO ())
 
-newtype Trigger a = Trigger (IPythonWidget (SuitableWidget a) -> IO ())
-
  
 data RequiredWidget a where
         RequiredWidget ::
@@ -107,11 +98,8 @@
 extractEventSetter :: WidgetConf x -> EventSetter x
 extractEventSetter (WidgetConf wr) = EventSetter $ setEvent wr
 
-extractTrigger :: WidgetConf x -> Trigger x
-extractTrigger (WidgetConf wr) = Trigger $ trigger wr
-
 extractInitializer :: WidgetConf x -> Initializer x
-extractInitializer (WidgetConf wr) = Initializer initializer
+extractInitializer WidgetConf{} = Initializer initializer
 
 createWidget :: Constructor a -> IO (RequiredWidget a)
 createWidget (Constructor con) = fmap RequiredWidget con
@@ -146,7 +134,6 @@
       getters = rmap extractGetter rc
       eventSetters = rmap extractEventSetter rc
       initializers = rmap extractInitializer rc
-      triggers = rmap extractTrigger rc
 
   bx <- mkFlexBox
   out <- mkOutputWidget
@@ -188,14 +175,8 @@
 getValue :: WrappedWidget w h f a -> IPythonWidget w -> IO a
 getValue (WrappedWidget _ _ field) widget = getField widget field
 
-setValue :: WrappedWidget w h f a -> IPythonWidget w -> a -> IO ()
-setValue (WrappedWidget _ _ field) widget = setField widget field
-
 setEvent :: WrappedWidget w h f a -> IPythonWidget w -> IO () -> IO ()
 setEvent (WrappedWidget _ h _) widget = setField widget h
-
-trigger :: WrappedWidget w h f a -> IPythonWidget w -> IO ()
-trigger (WrappedWidget _ h _) = triggerEvent h
 
 class RecAll Attr (WidgetFields (SuitableWidget a)) ToPairs => FromWidget a where
   type SuitableWidget a :: WidgetType
diff --git a/src/IHaskell/Display/Widgets/Output.hs b/src/IHaskell/Display/Widgets/Output.hs
--- a/src/IHaskell/Display/Widgets/Output.hs
+++ b/src/IHaskell/Display/Widgets/Output.hs
@@ -18,12 +18,8 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
-import           Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
-import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/Selection/Dropdown.hs b/src/IHaskell/Display/Widgets/Selection/Dropdown.hs
--- a/src/IHaskell/Display/Widgets/Selection/Dropdown.hs
+++ b/src/IHaskell/Display/Widgets/Selection/Dropdown.hs
@@ -12,7 +12,7 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
+import           Control.Monad (void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
diff --git a/src/IHaskell/Display/Widgets/Selection/RadioButtons.hs b/src/IHaskell/Display/Widgets/Selection/RadioButtons.hs
--- a/src/IHaskell/Display/Widgets/Selection/RadioButtons.hs
+++ b/src/IHaskell/Display/Widgets/Selection/RadioButtons.hs
@@ -12,12 +12,11 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
+import           Control.Monad (when, void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
 import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/Selection/SelectMultiple.hs b/src/IHaskell/Display/Widgets/Selection/SelectMultiple.hs
--- a/src/IHaskell/Display/Widgets/Selection/SelectMultiple.hs
+++ b/src/IHaskell/Display/Widgets/Selection/SelectMultiple.hs
@@ -12,13 +12,12 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (fmap, join, sequence, void)
+import           Control.Monad (void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
 import           Data.Text (Text)
 import qualified Data.Vector as V
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/Selection/ToggleButtons.hs b/src/IHaskell/Display/Widgets/Selection/ToggleButtons.hs
--- a/src/IHaskell/Display/Widgets/Selection/ToggleButtons.hs
+++ b/src/IHaskell/Display/Widgets/Selection/ToggleButtons.hs
@@ -12,7 +12,7 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join, void)
+import           Control.Monad (void)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
diff --git a/src/IHaskell/Display/Widgets/Singletons.hs b/src/IHaskell/Display/Widgets/Singletons.hs
--- a/src/IHaskell/Display/Widgets/Singletons.hs
+++ b/src/IHaskell/Display/Widgets/Singletons.hs
@@ -13,7 +13,7 @@
 -- Widget properties
 singletons
   [d|
-
+   
   data Field = ViewModule
              | ViewName
              | ModelModule
diff --git a/src/IHaskell/Display/Widgets/String/HTML.hs b/src/IHaskell/Display/Widgets/String/HTML.hs
--- a/src/IHaskell/Display/Widgets/String/HTML.hs
+++ b/src/IHaskell/Display/Widgets/String/HTML.hs
@@ -12,11 +12,8 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
 import           Data.IORef (newIORef)
-import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/String/Latex.hs b/src/IHaskell/Display/Widgets/String/Latex.hs
--- a/src/IHaskell/Display/Widgets/String/Latex.hs
+++ b/src/IHaskell/Display/Widgets/String/Latex.hs
@@ -12,11 +12,8 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
 import           Data.IORef (newIORef)
-import           Data.Text (Text)
-import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
 import           IHaskell.Eval.Widgets
diff --git a/src/IHaskell/Display/Widgets/String/Text.hs b/src/IHaskell/Display/Widgets/String/Text.hs
--- a/src/IHaskell/Display/Widgets/String/Text.hs
+++ b/src/IHaskell/Display/Widgets/String/Text.hs
@@ -12,11 +12,10 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
+import           Control.Monad (when)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as Map
 import           Data.IORef (newIORef)
-import           Data.Text (Text)
 import           Data.Vinyl (Rec(..), (<+>))
 
 import           IHaskell.Display
diff --git a/src/IHaskell/Display/Widgets/String/TextArea.hs b/src/IHaskell/Display/Widgets/String/TextArea.hs
--- a/src/IHaskell/Display/Widgets/String/TextArea.hs
+++ b/src/IHaskell/Display/Widgets/String/TextArea.hs
@@ -12,7 +12,6 @@
 -- To keep `cabal repl` happy when running from the ihaskell repo
 import           Prelude
 
-import           Control.Monad (when, join)
 import           Data.Aeson
 import qualified Data.HashMap.Strict as HM
 import           Data.IORef (newIORef)
diff --git a/src/IHaskell/Display/Widgets/Types.hs b/src/IHaskell/Display/Widgets/Types.hs
--- a/src/IHaskell/Display/Widgets/Types.hs
+++ b/src/IHaskell/Display/Widgets/Types.hs
@@ -12,6 +12,8 @@
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE ExistentialQuantification #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE AutoDeriveTypeable #-}
 
 module IHaskell.Display.Widgets.Types where
 
@@ -48,8 +50,8 @@
 --
 -- The IPython widgets expect state updates of the form {"property": value}, where an empty string
 -- for numeric values is ignored by the frontend and the default value is used instead. Some numbers
--- need to be sent as numbers (represented by @Integer@), whereas some need to be sent as Strings
--- (@StrInt@).
+-- need to be sent as numbers (represented by @Integer@), whereas some (css lengths) need to be sent
+-- as Strings (@PixCount@).
 --
 -- Child widgets are expected to be sent as strings of the form "IPY_MODEL_<uuid>", where @<uuid>@
 -- represents the uuid of the widget's comm.
@@ -58,19 +60,19 @@
 -- look at the supplied MsgSpec.md.
 --
 -- Widgets are not able to do console input, the reason for that can be found in the messaging
--- specification
-import           Control.Monad (unless, join, when, void, mapM_)
+-- specification.
+import           Control.Monad (unless, join, when, void)
 import           Control.Applicative ((<$>))
 import qualified Control.Exception as Ex
-
-import           GHC.IO.Exception
+import           Data.Typeable (Typeable, TypeRep, typeOf)
+import           Data.IORef (IORef, readIORef, modifyIORef)
+import           Data.Text (Text, pack)
 import           System.IO.Error
 import           System.Posix.IO
+import           Text.Printf (printf)
 
 import           Data.Aeson
 import           Data.Aeson.Types (Pair)
-import           Data.IORef (IORef, readIORef, modifyIORef)
-import           Data.Text (Text, pack)
 
 import           Data.Vinyl (Rec(..), (<+>), recordToList, reifyConstraint, rmap, Dict(..))
 import           Data.Vinyl.Functor (Compose(..), Const(..))
@@ -80,11 +82,13 @@
 import           Data.Singletons.Prelude ((:++))
 import           Data.Singletons.TH
 
+import           GHC.IO.Exception
+
 import           IHaskell.Eval.Widgets (widgetSendUpdate)
 import           IHaskell.Display (Base64, IHaskellWidget(..))
 import           IHaskell.IPython.Message.UUID
 
-import           IHaskell.Display.Widgets.Singletons (Field, SField(..))
+import           IHaskell.Display.Widgets.Singletons (Field, SField)
 import qualified IHaskell.Display.Widgets.Singletons as S
 import           IHaskell.Display.Widgets.Common
 
@@ -140,19 +144,19 @@
         FieldType S.Visible = Bool
         FieldType S.CSS = [(Text, Text, Text)]
         FieldType S.DOMClasses = [Text]
-        FieldType S.Width = StrInt
-        FieldType S.Height = StrInt
-        FieldType S.Padding = StrInt
-        FieldType S.Margin = StrInt
+        FieldType S.Width = PixCount
+        FieldType S.Height = PixCount
+        FieldType S.Padding = PixCount
+        FieldType S.Margin = PixCount
         FieldType S.Color = Text
         FieldType S.BackgroundColor = Text
         FieldType S.BorderColor = Text
-        FieldType S.BorderWidth = StrInt
-        FieldType S.BorderRadius = StrInt
+        FieldType S.BorderWidth = PixCount
+        FieldType S.BorderRadius = PixCount
         FieldType S.BorderStyle = BorderStyleValue
         FieldType S.FontStyle = FontStyleValue
         FieldType S.FontWeight = FontWeightValue
-        FieldType S.FontSize = StrInt
+        FieldType S.FontSize = PixCount
         FieldType S.FontFamily = Text
         FieldType S.Description = Text
         FieldType S.ClickHandler = IO ()
@@ -220,7 +224,7 @@
   upperBound :: a
 
 -- Set according to what IPython widgets use
-instance CustomBounded StrInt where
+instance CustomBounded PixCount where
   upperBound = 10 ^ 16 - 1
   lowerBound = -(10 ^ 16 - 1)
 
@@ -312,7 +316,8 @@
                                             '[S.Orientation, S.ShowRange, S.ReadOut, S.SliderColor]
         WidgetFields BoxType = BoxClass
         WidgetFields ProxyType = WidgetClass :++ '[S.Child]
-        WidgetFields PlaceProxyType = WidgetFields ProxyType :++ '[S.Selector]
+        WidgetFields PlaceProxyType =
+                                    WidgetFields ProxyType :++ '[S.Selector]
         WidgetFields FlexBoxType =
                                  BoxClass :++ '[S.Orientation, S.Flex, S.Pack, S.Align]
         WidgetFields AccordionType = SelectionContainerClass
@@ -327,13 +332,16 @@
 unwrap (Real x) = x
 
 -- Wrapper around a field.
-data Attr (f :: Field) =
-       Attr
-         { _value :: AttrVal (FieldType f)
-         , _verify :: FieldType f -> IO (FieldType f)
-         , _field :: Field
-         }
+data Attr (f :: Field) where
+  Attr :: Typeable (FieldType f)
+       => { _value :: AttrVal (FieldType f)
+          , _verify :: FieldType f -> IO (FieldType f)
+          , _field :: Field
+          } -> Attr f
 
+getFieldType :: Attr f -> TypeRep
+getFieldType Attr { _value = attrval } = typeOf $ unwrap attrval
+
 instance ToJSON (FieldType f) => ToJSON (Attr f) where
   toJSON attr =
     case _value attr of
@@ -581,7 +589,7 @@
 
 -- | Store the value for a field, as an object parametrized by the Field. No verification is done
 -- for these values.
-(=::) :: SingI f => Sing f -> FieldType f -> Attr f
+(=::) :: (SingI f, Typeable (FieldType f)) => Sing f -> FieldType f -> Attr f
 s =:: x = Attr { _value = Real x, _verify = return, _field = reflect s }
 
 -- | If the number is in the range, return it. Otherwise raise the appropriate (over/under)flow
@@ -594,13 +602,13 @@
   | otherwise = error "The impossible happened in IHaskell.Display.Widgets.Types.rangeCheck"
 
 -- | Store a numeric value, with verification mechanism for its range.
-ranged :: (SingI f, Num (FieldType f), Ord (FieldType f))
+ranged :: (SingI f, Num (FieldType f), Ord (FieldType f), Typeable (FieldType f))
        => Sing f -> (FieldType f, FieldType f) -> AttrVal (FieldType f) -> Attr f
 ranged s range x = Attr x (rangeCheck range) (reflect s)
 
 -- | Store a numeric value, with the invariant that it stays non-negative. The value set is set as a
 -- dummy value if it's equal to zero.
-(=:+) :: (SingI f, Num (FieldType f), CustomBounded (FieldType f), Ord (FieldType f))
+(=:+) :: (SingI f, Num (FieldType f), CustomBounded (FieldType f), Ord (FieldType f), Typeable (FieldType f))
       => Sing f -> FieldType f -> Attr f
 s =:+ val = Attr
               ((if val == 0
@@ -837,9 +845,12 @@
 properties :: IPythonWidget w -> IO ()
 properties widget = do
   st <- readIORef $ state widget
-  let convert :: Attr f -> Const Field f
-      convert attr = Const { getConst = _field attr }
-  mapM_ print $ recordToList . rmap convert . _getState $ st
+  let convert :: Attr f -> Const (Field, TypeRep) f
+      convert attr = Const (_field attr, getFieldType attr)
+
+      renderRow (fname, ftype) = printf "%s ::: %s" (show fname) (show ftype)
+      rows = map renderRow . recordToList . rmap convert $ _getState st
+  mapM_ putStrLn rows
 
 -- Helper function for widget to enforce their inability to fetch console input
 noStdin :: IO a -> IO ()