Use cartesianProduct instead of setProduct where possible (#112)

* remove setProduct, use cartesianProduct (fixes #111)

* conditional setProduct via CPP (fixes #111)

src/Algebra/Graph/Relation/Internal.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module     : Algebra.Graph.Relation.Internal
@@ -171,7 +172,11 @@ instance NFData a => NFData (Relation a) where
 
 -- | Compute the Cartesian product of two sets. /Note: this function is for internal use only/.
 setProduct :: Set a -> Set b -> Set (a, b)
+#if MIN_VERSION_containers(0,5,11)
+setProduct = Set.cartesianProduct
+#else
 setProduct x y = Set.fromDistinctAscList [ (a, b) | a <- Set.toAscList x, b <- Set.toAscList y ]
+#endif
 
 instance (Ord a, Num a) => Num (Relation a) where
     fromInteger = vertex . fromInteger