Added the X.L.StateFull module providing the StateFull layout and the FocusTracking layout transformer.

CHANGES.md

@@ -76,6 +76,15 @@
 
 ### New Modules
 
+  * `XMonad.Layout.StateFull`
+
+    Provides StateFull: a stateful form of Full that does not misbehave when
+    floats are focused, and the FocusTracking layout transformer by means of
+    which StateFull is implemented. FocusTracking simply holds onto the last
+    true focus it was given and continues to use it as the focus for the
+    transformed layout until it sees another. It can be used to improve the
+    behaviour of a child layout that has not been given the focused window.
+
   * `XMonad.Hooks.Focus`
 
     A new module extending ManageHook EDSL to work on focused windows and

XMonad/Layout/StateFull.hs

@@ -0,0 +1,95 @@
+{-# LANGUAGE FlexibleInstances, FlexibleContexts, MultiParamTypeClasses #-}
+{-# LANGUAGE PatternSynonyms #-}
+
+--------------------------------------------------------------------------------
+-- |
+-- Module      :  XMonad.Layout.StateFull
+-- Description :  The StateFull Layout & FocusTracking Layout Transformer
+-- Copyright   :  (c) 2018  L. S. Leary
+-- License     :  BSD3-style (see LICENSE)
+--
+-- Maintainer  :  L. S. Leary
+-- Stability   :  unstable
+-- Portability :  unportable
+--
+-- Provides StateFull: a stateful form of Full that does not misbehave when
+-- floats are focused, and the FocusTracking layout transformer by means of
+-- which StateFull is implemented. FocusTracking simply holds onto the last
+-- true focus it was given and continues to use it as the focus for the
+-- transformed layout until it sees another. It can be used to improve the
+-- behaviour of a child layout that has not been given the focused window.
+--------------------------------------------------------------------------------
+
+module XMonad.Layout.StateFull (
+  -- * Usage
+  -- $Usage
+  pattern StateFull,
+  StateFull,
+  FocusTracking(..),
+  focusTracking
+) where
+
+import XMonad hiding ((<&&>))
+import qualified XMonad.StackSet as W
+import XMonad.Util.Stack (findZ)
+
+import Data.Maybe (fromMaybe)
+import Control.Applicative ((<|>))
+import Control.Monad (join)
+
+-- $Usage
+--
+-- To use it, first you need to:
+--
+-- > import XMonad.Layout.StateFull
+--
+-- Then to toggle your tiled layout with @StateFull@, you can do:
+--
+-- > main = xmonad def { layoutHook = someTiledLayout ||| StateFull }
+--
+-- Or, some child layout that depends on focus information can be made to fall
+-- back on the last focus it had:
+--
+-- > main = xmonad def
+-- >  { layoutHook = someParentLayoutWith aChild (focusTracking anotherChild) }
+
+-- | The @FocusTracking@ data type for which the @LayoutClass@ instance is
+--   provided.
+data FocusTracking l a = FocusTracking (Maybe a) (l a)
+  deriving (Show, Read)
+
+-- | Transform a layout into one that remembers and uses its last focus.
+focusTracking :: l a -> FocusTracking l a
+focusTracking = FocusTracking Nothing
+
+-- | A type synonym to match the @StateFull@ pattern synonym.
+type StateFull = FocusTracking Full
+
+-- | A pattern synonym for the primary use case of the @FocusTracking@
+--   transformer; using @Full@.
+pattern StateFull :: StateFull a
+pattern StateFull = FocusTracking Nothing Full
+
+instance LayoutClass l Window => LayoutClass (FocusTracking l) Window where
+
+  description (FocusTracking _ child)
+    | (chDesc == "Full")  = "StateFull"
+    | (' ' `elem` chDesc) = "FocusTracking (" ++ chDesc ++ ")"
+    | otherwise           = "FocusTracking " ++ chDesc
+    where chDesc = description child
+
+  runLayout (W.Workspace i (FocusTracking mOldFoc childL) mSt) sr = do
+
+    mRealFoc <- gets (W.peek . windowset)
+    let mGivenFoc = W.focus <$> mSt
+        passedMSt = if mRealFoc == mGivenFoc then mSt
+                    else join (mOldFoc >>= \oF -> findZ (==oF) mSt) <|> mSt
+
+    (wrs, mChildL') <- runLayout (W.Workspace i childL passedMSt) sr
+    let newFT = if mRealFoc /= mGivenFoc then FocusTracking mOldFoc <$> mChildL'
+                else Just $ FocusTracking mGivenFoc (fromMaybe childL mChildL')
+
+    return (wrs, newFT)
+
+  handleMessage (FocusTracking mf childLayout) m =
+    (fmap . fmap) (FocusTracking mf) (handleMessage childLayout m)

xmonad-contrib.cabal

@@ -273,6 +273,7 @@ library
                         XMonad.Layout.Spiral
                         XMonad.Layout.Square
                         XMonad.Layout.StackTile
+                        XMonad.Layout.StateFull
                         XMonad.Layout.Stoppable
                         XMonad.Layout.SubLayouts
                         XMonad.Layout.TabBarDecoration