X.H.Modal: Add support for EZConfig-style bindings

Add support for EZConfig-style bindings while also maintaining some
guarantees as to which type of representation we will store in the
extensible state.  This means that parsing of the keys will happen no
later than the call to `modal`.

Users can choose to use `mkKeysEz` or `mkKeysFun` to create a new
collection of keys to bind for a mode.  This is deemed more ergonomic
than exporting the respective constructors directly.

XMonad/Hooks/Modal.hs

@@ -1,5 +1,4 @@
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
-{-# LANGUAGE InstanceSigs #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE NamedFieldPuns #-}
 
@@ -28,6 +27,7 @@ module XMonad.Hooks.Modal
   , modeWithExit
   , mode
   , Mode
+  , mkKeysEz
   , setMode
   , exitMode
  -- * Provided Modes #ProvidedModes#
@@ -50,7 +50,6 @@ import           XMonad
 import           Data.Bits                     ( (.&.)
                                                , complement
                                                )
-import           Data.Coerce                   ( coerce )
 import           Data.List
 import qualified Data.Map.Strict               as M
 -- contrib
@@ -58,10 +57,14 @@ import           XMonad.Actions.FloatKeys      ( keysMoveWindow
                                                , keysResizeWindow
                                                )
 import           XMonad.Prelude
+import           XMonad.Util.EZConfig          ( parseKeyCombo
+                                               , mkKeymap
+                                               )
 import qualified XMonad.Util.ExtensibleConf    as XC
 import qualified XMonad.Util.ExtensibleState   as XS
 import           XMonad.Util.Grab
 import           XMonad.Util.Loggers
+import           XMonad.Util.Parser            ( runParser )
 
 -- }}}
 
@@ -107,10 +110,21 @@ import           XMonad.Util.Loggers
 
 -- --< Types >-- {{{
 
+-- | Internally, we represent keys as the usual function type:
+-- @XConfig Layout -> M.Map (ButtonMask, KeySym) (X ())@.
+type Keys = XConfig Layout -> M.Map (ButtonMask, KeySym) (X ())
+
+-- | From a list of 'XMonad.Util.EZConfig'-style bindings, generate a
+-- key representation.
+--
+-- >>> mkKeysEz [("h", xmessage "Hello, world!")]
+mkKeysEz :: [(String, X ())] -> Keys
+mkKeysEz = flip mkKeymap
+
 -- | The mode type. Use 'mode' or 'modeWithExit' to create modes.
 data Mode = Mode
   { label     :: !String
-  , boundKeys :: !(XConfig Layout -> M.Map (ButtonMask, KeySym) (X ()))
+  , boundKeys :: !Keys
   }
 
 -- | Newtype for the extensible config.
@@ -174,17 +188,15 @@ modal modes = XC.once
 
 -- | Create a 'Mode' from the given binding to 'exitMode', label and
 -- keybindings.
-modeWithExit
+modeWithExit :: String -> String -> Keys -> Mode
-  :: (ButtonMask, KeySym)
+modeWithExit exitKey mlabel keys = Mode mlabel $ \cnf ->
-  -> String
+  let exit = fromMaybe (0, xK_Escape) $ runParser (parseKeyCombo cnf) exitKey
-  -> (XConfig Layout -> M.Map (ButtonMask, KeySym) (X ()))
+   in M.insert exit exitMode (keys cnf)
-  -> Mode
-modeWithExit exitKey mlabel keysF = Mode mlabel (M.insert exitKey exitMode . keysF)
 
 -- | Create a 'Mode' from the given label and keybindings. Sets the
 -- @escape@ key to 'exitMode'.
-mode :: String -> (XConfig Layout -> M.Map (ButtonMask, KeySym) (X ())) -> Mode
+mode :: String -> Keys -> Mode
-mode = modeWithExit (noModMask, xK_Escape)
+mode = modeWithExit "<Escape>"
 
 -- | Set the current 'Mode' based on its label.
 setMode :: String -> X ()
@@ -265,7 +277,7 @@ overlay
   :: String  -- ^ Label for the new mode
   -> Mode -- ^ Base mode
   -> Mode
-overlay label m = Mode label $ \cnf -> boundKeys m cnf `M.union` keys cnf cnf
+overlay label m = Mode label $ \cnf -> boundKeys m cnf <> keys cnf cnf
 
 -- | Strips the modifier key from the provided keybindings.
 stripModifier