core: creating a new graph from another graph

lib/rdf/graph.ex

@@ -38,6 +38,12 @@ defmodule RDF.Graph do
   def new(%RDF.Description{} = description),
     do: new() |> add(description)
 
+  @doc """
+  Creates an unnamed `RDF.Graph` from another `RDF.Graph`.
+  """
+  def new(%RDF.Graph{descriptions: descriptions}),
+    do: %RDF.Graph{descriptions: descriptions}
+
   @doc """
   Creates an empty unnamed `RDF.Graph`.
   """
@@ -68,6 +74,12 @@ defmodule RDF.Graph do
   def new(name, %RDF.Description{} = description),
     do: new(name) |> add(description)
 
+  @doc """
+  Creates a named `RDF.Graph` from another `RDF.Graph`.
+  """
+  def new(name, %RDF.Graph{descriptions: descriptions}),
+    do: %RDF.Graph{new(name) | descriptions: descriptions}
+
   @doc """
   Creates an unnamed `RDF.Graph` with initial triples.
   """

test/unit/graph_test.exs

@@ -77,6 +77,26 @@ defmodule RDF.GraphTest do
       assert unnamed_graph?(g)
       assert graph_includes_statement?(g, {EX.Subject, EX.predicate, EX.Object})
     end
+
+    test "creating a named graph from another graph" do
+      g = Graph.new(EX.GraphName, Graph.new({EX.Subject, EX.predicate, EX.Object}))
+      assert named_graph?(g, uri(EX.GraphName))
+      assert graph_includes_statement?(g, {EX.Subject, EX.predicate, EX.Object})
+
+      g = Graph.new(EX.GraphName, Graph.new(EX.OtherGraphName, {EX.Subject, EX.predicate, EX.Object}))
+      assert named_graph?(g, uri(EX.GraphName))
+      assert graph_includes_statement?(g, {EX.Subject, EX.predicate, EX.Object})
+    end
+
+    test "creating an unnamed graph from another graph" do
+      g = Graph.new(Graph.new({EX.Subject, EX.predicate, EX.Object}))
+      assert unnamed_graph?(g)
+      assert graph_includes_statement?(g, {EX.Subject, EX.predicate, EX.Object})
+
+      g = Graph.new(Graph.new(EX.OtherGraphName, {EX.Subject, EX.predicate, EX.Object}))
+      assert unnamed_graph?(g)
+      assert graph_includes_statement?(g, {EX.Subject, EX.predicate, EX.Object})
+    end
   end
 
   describe "adding triples" do