Working (but slow) shadow shapes

src/Shape/Data.hs

@@ -4,10 +4,16 @@ module Shape.Data
     where
 import Geometry.Data
 import Control.Lens
+--import Data.Monoid
 data Shape = Shape
     { _shVertices :: [ShapeV]
     , _shEdges    :: [Point3]
     }
+instance Semigroup Shape where
+    (<>) (Shape sv1 se1) (Shape sv2 se2) = Shape (sv1 ++ sv2) (se1 ++ se2)
+instance Monoid Shape where
+    mempty = Shape [] []
+
 -- edges are given by four consecutive points
 data ShapeV = ShapeV
     { _svPos :: Point3