put margins on Hamming widget

src/Hamming/App/Widgets/Internal.hs

@@ -24,6 +24,8 @@ License along with this program.  If not, see
 
 |-}
 
+{-# LANGUAGE TupleSections #-}
+
 module Hamming.App.Widgets.Internal (hammingW') where
 
 import Data.Bits ((.&.))
@@ -33,6 +35,15 @@ import Hamming.App.Types
 
 hammingW' :: AppState -> [[([String], Char)]]
 hammingW' state = let
+  header = ([], ' ') : map (["margin"],) ['0'..'3']
+  body   = hammingBody state
+  in header : zipWith
+    (\n row -> (["margin"], n) : row)
+    ['0'..'3']
+    body
+
+hammingBody :: AppState -> [[([String], Char)]]
+hammingBody state = let
   code = state^.hammingCode
   in map
   ( map