Add RDF.Graph.annotations/1

lib/rdf/graph.ex

@@ -636,6 +636,21 @@ defmodule RDF.Graph do
     Map.values(graph.descriptions)
   end
 
+  @doc """
+  Returns the `RDF.Graph` of all annotations.
+
+  Note: The graph includes only triples where the subject is a quoted triple.
+  Triples where only the object is a quoted triple are NOT included.
+  """
+  @spec annotations(t) :: t
+  def annotations(%__MODULE__{} = graph) do
+    %__MODULE__{
+      graph
+      | descriptions:
+          for(annotation = {{_, _, _}, _} <- graph.descriptions, into: %{}, do: annotation)
+    }
+  end
+
   @doc """
   Gets and updates the description of the given subject, in a single pass.
 

test/unit/star/graph_test.exs

@@ -715,6 +715,20 @@ defmodule RDF.Star.Graph.Test do
     end
   end
 
+  describe "annotations/1" do
+    test "when no annotations exist" do
+      assert Graph.annotations(graph()) == graph()
+    end
+
+    test "when annotations exist" do
+      assert Graph.annotations(graph_with_annotation()) == graph_with_annotation()
+
+      assert graph_with_annotation()
+             |> Graph.add(statement())
+             |> Graph.annotations() == graph_with_annotation()
+    end
+  end
+
   test "include?/3" do
     assert Graph.include?(graph_with_annotations(), star_statement())
     assert Graph.include?(graph_with_annotations(), {EX.As, EX.ap(), statement()})