Some finishing touches to the 4.0 support

* [BUGFIX]: Fix bug with width, height etc. values

The values needed to be explicitly sent as "<value>(px/em/...)" strings.
Solved by assuming "px" for all values.

* Updated messaging specification documentation as necessary.

ihaskell-display/ihaskell-widgets/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 @@ The initial state update must *at least* have the following fields:
 
   - 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 @@ If this were not so, the frontend would not be able to determine under which cel
 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.
 
 ---
 

ihaskell-display/ihaskell-widgets/src/IHaskell/Display/Widgets/Common.hs

@@ -97,11 +97,11 @@ pattern Selector = S.SSelector
 closeWidget :: IHaskellWidget w => w -> IO ()
 closeWidget w = widgetSendClose w emptyObject
 
-newtype StrInt = StrInt Integer
+newtype PixCount = PixCount Integer
   deriving (Num, Ord, Eq, Enum)
 
-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

ihaskell-display/ihaskell-widgets/src/IHaskell/Display/Widgets/Types.hs

@@ -48,8 +48,8 @@ module IHaskell.Display.Widgets.Types where
 --
 -- 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.
@@ -58,7 +58,7 @@ module IHaskell.Display.Widgets.Types where
 -- 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
+-- specification.
 import           Control.Monad (unless, join, when, void, mapM_)
 import           Control.Applicative ((<$>))
 import qualified Control.Exception as Ex
@@ -140,19 +140,19 @@ type family FieldType (f :: Field) :: * where
         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 +220,7 @@ class CustomBounded a where
   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)