Allow for items to cast shadows

src/ShapePicture/Data.hs

@@ -4,8 +4,16 @@ module ShapePicture.Data
     where
 import Shape
 import Picture
+import Control.Lens
 data SPic = SPic 
     { _spShape :: Shape 
     , _spPicture :: Picture
     }
 
+instance Semigroup SPic where
+    (<>) (SPic a b) (SPic x y) = SPic (a <> x) (b <>y)
+
+instance Monoid SPic where
+    mempty = SPic emptySH blank
+
+makeLenses ''SPic