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+{-# LANGUAGE ScopedTypeVariables #-}
+module Instances where
+
+import Test.QuickCheck
+
+import Utils
+
+import XMonad.StackSet
+import Control.Monad
+import Data.List (nub, genericLength)
+
+import Debug.Trace
+
+--
+-- The all important Arbitrary instance for StackSet.
+--
+instance (Integral i, Integral s, Eq a, Arbitrary a, Arbitrary l, Arbitrary sd)
+         => Arbitrary (StackSet i l a s sd) where
+  arbitrary = do
+      -- TODO: Fix this to be a reasonable higher number, Possibly use PositiveSized
+      numWs        <- choose (1, 20)    -- number of workspaces, there must be at least 1.
+      numScreens   <- choose (1, numWs) -- number of physical screens, there must be at least 1
+      lay <- arbitrary                  -- pick any layout
+
+      wsIdxInFocus <- choose (1, numWs) -- pick index of WS to be in focus
+
+      -- The same screen id's will be present in the list, with high possibility.
+      screens  <- replicateM numScreens arbitrary
+
+      -- Generate a list of "windows" for each workspace.
+      wsWindows  <- vector numWs :: Gen [[a]]
+
+      -- Pick a random window "number" in each workspace, to give focus.
+      focus <- sequence [ if null windows
+                          then return Nothing
+                          else liftM Just $ choose (0, length windows - 1)
+                        | windows <- wsWindows ]
+
+      let tags = [1 .. fromIntegral numWs]
+          focusWsWindows = zip focus wsWindows
+          wss = zip tags focusWsWindows -- tmp representation of a workspace (tag, windows)
+          initSs = new lay tags screens
+      return $
+        view (fromIntegral wsIdxInFocus) $
+        foldr (\(tag, (focus, windows)) ss -> -- Fold through all generated (tags,windows).
+                -- set workspace active by tag and fold through all
+                -- windows while inserting them.  Apply the given number
+                -- of `focusUp` on the resulting StackSet.
+                applyN focus focusUp $ foldr insertUp (view tag ss) windows
+              ) initSs wss
+
+
+--
+-- Just generate StackSets with Char elements.
+--
+type Tag = Int
+type Window = Char
+type T = StackSet Tag Int Window Int Int
+
+
+
+newtype EmptyStackSet = EmptyStackSet T
+    deriving Show
+
+instance Arbitrary EmptyStackSet where
+    arbitrary = do
+        (NonEmptyNubList ns)  <- arbitrary
+        (NonEmptyNubList sds) <- arbitrary
+        l <- arbitrary
+        -- there cannot be more screens than workspaces:
+        return . EmptyStackSet . new l ns $ take (min (length ns) (length sds)) sds
+
+
+
+newtype NonEmptyWindowsStackSet = NonEmptyWindowsStackSet T
+    deriving Show
+
+instance Arbitrary NonEmptyWindowsStackSet where
+  arbitrary =
+    NonEmptyWindowsStackSet `fmap` (arbitrary `suchThat` (not . null . allWindows))
+
+
+
+newtype SizedPositive = SizedPositive Int
+    deriving (Eq, Ord, Show, Read)
+
+instance Arbitrary SizedPositive where
+  arbitrary = sized $ \s -> do x <- choose (1, max 1 s)
+                               return $ SizedPositive x
+
+
+
+newtype NonEmptyNubList a = NonEmptyNubList [a]
+    deriving ( Eq, Ord, Show, Read )
+
+instance (Eq a, Arbitrary a) => Arbitrary (NonEmptyNubList a) where
+  arbitrary   = NonEmptyNubList `fmap` ((liftM nub arbitrary) `suchThat` (not . null))
+
+
+
+-- | Pull out an arbitrary tag from the StackSet. This removes the need for the
+-- precondition "n `tagMember x` in many properties and thus reduces the number
+-- of discarded tests.
+--
+--  n <- arbitraryTag x
+--
+-- We can do the reverse with a simple `suchThat`:
+--
+-- n <- arbitrary `suchThat` \n' -> not $ n' `tagMember` x
+arbitraryTag :: T -> Gen Tag
+arbitraryTag x = do
+  let ts = tags x
+  -- There must be at least 1 workspace, thus at least 1 tag.
+  idx <- choose (0, (length ts) - 1)
+  return $ ts!!idx
+
+-- | Pull out an arbitrary window from a StackSet that is guaranteed to have a
+-- non empty set of windows. This eliminates the precondition "i `member` x" in
+-- a few properties.
+--
+--
+-- foo (nex :: NonEmptyWindowsStackSet) = do
+--   let NonEmptyWindowsStackSet x = nex
+--   w <- arbitraryWindow nex
+--   return $ .......
+--
+-- We can do the reverse with a simple `suchThat`:
+--
+--   n <- arbitrary `suchThat` \n' -> not $ n `member` x
+arbitraryWindow :: NonEmptyWindowsStackSet -> Gen Window
+arbitraryWindow (NonEmptyWindowsStackSet x) = do
+  let ws = allWindows x
+  -- We know that there are at least 1 window in a NonEmptyWindowsStackSet.
+  idx <- choose(0, (length ws) - 1)
+  return $ ws!!idx