make the check for overflow cleaner

tests/Properties.hs

@@ -35,7 +35,7 @@ main = do
             Success {} -> return True
             _ -> return False
       perform (s, t) = printf "%-35s: " s >> qc t
-  n <- length . filter not ok <$> mapM perform tests
+  n <- length . filter not <$> mapM perform tests
   unless (n == 0) (error (show n ++ " test(s) failed"))
 
 
@@ -167,8 +167,8 @@ tests =
 
   ,("tile 1 window fullsize", property prop_tile_fullscreen)
   ,("tiles never overlap",    property prop_tile_non_overlap)
-  ,("split hozizontally",     property prop_split_hoziontal)
-  ,("split verticalBy",       property prop_splitVertically)
+  ,("split horizontal",       property prop_split_horizontal)
+  ,("split vertical",         property prop_split_vertical)
 
   ,("pure layout tall",       property prop_purelayout_tall)
   ,("send shrink    tall",    property prop_shrink_tall)

tests/Properties/Layout/Tall.hs

@@ -28,7 +28,8 @@ prop_tile_non_overlap rect windows nmaster = noOverlaps (tile pct rect nmaster w
         pct = 3 % 100
 
 -- splitting horizontally yields sensible results
-prop_split_hoziontal (NonNegative n) x =
+prop_split_horizontal (NonNegative n) x =
+      (noOverflows (+) (rect_x x) (rect_width x)) ==>
         sum (map rect_width xs) == rect_width x
      &&
         all (== rect_height x) (map rect_height xs)
@@ -38,9 +39,8 @@ prop_split_hoziontal (NonNegative n) x =
     where
         xs = splitHorizontally n x
 
--- splitting horizontally yields sensible results
-prop_splitVertically (r :: Rational) x =
-
+-- splitting vertically yields sensible results
+prop_split_vertical (r :: Rational) x =
         rect_x x == rect_x a && rect_x x == rect_x b
       &&
         rect_width x == rect_width a && rect_width x == rect_width b

tests/Properties/Screen.hs

@@ -1,6 +1,7 @@
 {-# LANGUAGE ScopedTypeVariables #-}
 module Properties.Screen where
 
+import Utils
 import Test.QuickCheck
 import Instances
 
@@ -53,8 +54,8 @@ prop_aspect_hint_shrink hint (w,h) = case applyAspectHint hint (w,h) of
 prop_aspect_fits =
     forAll ((,,,) <$> pos <*> pos <*> pos <*> pos) $ \ (x,y,a,b) -> 
     let f v = applyAspectHint ((x, y+a), (x+b, y)) v
-        overflow = or [ mul x (y+a), mul (x+b) y ]
-    in  not overflow ==> f (x,y) == (x,y)
+    in  and [ noOverflows (*) x (y+a), noOverflows (*) (x+b) y ]
+            ==> f (x,y) == (x,y)
 
   where pos = choose (0, 65535)
         mul a b = toInteger (a*b) /= toInteger a * toInteger b
@@ -65,10 +66,8 @@ prop_point_within r @ (Rectangle x y w h) =
               choose (0, fromIntegral h - 1)) $
         \(dx,dy) ->
     and [ dx > 0, dy > 0,
-         noOverflow x w,
-         noOverflow y h ]
+         noOverflows (\ a b -> a + abs b) x w,
+         noOverflows (\ a b -> a + abs b) y h ]
       ==> pointWithin (x+dx) (y+dy) r
-  where
-    noOverflow a b = (a + fromIntegral (abs b)) > a
 
 prop_point_within_mirror r (x,y) = pointWithin x y r == pointWithin y x (mirrorRect r)

tests/Utils.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE RankNTypes #-}
 module Utils where
 
 import XMonad.StackSet hiding (filter)
@@ -35,5 +36,12 @@ applyN Nothing f v = v
 applyN (Just 0) f v = v
 applyN (Just n) f v = applyN (Just $ n-1) f (f v)
 
-
 tags x = map tag $ workspaces x
+
+
+-- | noOverflows op a b is True if @a `op` fromIntegral b@ overflows (or
+-- otherwise gives the same answer when done using Integer
+noOverflows :: (Integral b, Integral c) =>
+  (forall a. Integral a => a -> a -> a) -> b -> c -> Bool
+noOverflows op a b = toInteger (a `op` fromIntegral b) == toInteger a `op` toInteger b
+