Various refactoring

src/Geometry.hs

@@ -191,12 +191,18 @@ doublePair (x,y) = [(x,y),(y,x)]
 doubleV2 :: V2 a -> [V2 a]
 doubleV2 (V2 x y) = [V2 x y,V2 y x]
 -- split a list into triples, forms triangles from a polygon
-polyToTris :: [s] -> [s]
-{-# INLINE polyToTris #-}
-polyToTris (a:as) = go a as
+polyToTris'' :: [s] -> [s]
+polyToTris'' (a:as) = go a as
   where
     go !x (y:z:ys) = x : y : z : go x (z:ys)
     go _ _ = []
+polyToTris'' _ = []
+
+polyToTris :: [s] -> [s]
+{-# INLINABLE polyToTris #-}
+polyToTris (x:xs) = foldr (f x) [] $ zip xs $ tail xs
+  where
+    f a (b,c) ls = a:b:c:ls
 polyToTris _ = []
 
 polyToTris' :: [s] -> [s]