Fix failing CI on Elixir 1.9

lib/rdf/dataset.ex

@@ -880,9 +880,13 @@ defmodule RDF.Dataset do
     def member?(dataset, statement), do: {:ok, Dataset.include?(dataset, statement)}
     def count(dataset), do: {:ok, Dataset.statement_count(dataset)}
 
-    def slice(dataset) do
-      size = Dataset.statement_count(dataset)
-      {:ok, size, &Enumerable.List.slice(Dataset.statements(dataset), &1, &2, size)}
+    if Version.match?(System.version(), "~> 1.10") do
+      def slice(dataset) do
+        size = Dataset.statement_count(dataset)
+        {:ok, size, &Enumerable.List.slice(Dataset.statements(dataset), &1, &2, size)}
+      end
+    else
+      def slice(_), do: {:error, __MODULE__}
     end
 
     def reduce(dataset, acc, fun) do

lib/rdf/description.ex

@@ -828,9 +828,13 @@ defmodule RDF.Description do
 
     def count(desc), do: {:ok, Description.statement_count(desc)}
 
-    def slice(desc) do
-      size = Description.statement_count(desc)
-      {:ok, size, &Enumerable.List.slice(Description.triples(desc), &1, &2, size)}
+    if Version.match?(System.version(), "~> 1.10") do
+      def slice(desc) do
+        size = Description.statement_count(desc)
+        {:ok, size, &Enumerable.List.slice(Description.triples(desc), &1, &2, size)}
+      end
+    else
+      def slice(_), do: {:error, __MODULE__}
     end
 
     def reduce(desc, acc, fun) do

lib/rdf/graph.ex

@@ -1093,9 +1093,13 @@ defmodule RDF.Graph do
     def member?(graph, triple), do: {:ok, Graph.include?(graph, triple)}
     def count(graph), do: {:ok, Graph.statement_count(graph)}
 
-    def slice(graph) do
-      size = Graph.statement_count(graph)
-      {:ok, size, &Enumerable.List.slice(Graph.triples(graph), &1, &2, size)}
+    if Version.match?(System.version(), "~> 1.10") do
+      def slice(graph) do
+        size = Graph.statement_count(graph)
+        {:ok, size, &Enumerable.List.slice(Graph.triples(graph), &1, &2, size)}
+      end
+    else
+      def slice(_), do: {:error, __MODULE__}
     end
 
     def reduce(graph, acc, fun) do

test/unit/dataset_test.exs

@@ -1829,6 +1829,11 @@ defmodule RDF.DatasetTest do
       assert ds ==
                Enum.reduce(ds, dataset(), fn statement, acc -> acc |> Dataset.add(statement) end)
     end
+
+    test "Enum.at (for Enumerable.slice/1)" do
+      assert Dataset.new({EX.S, EX.p(), EX.O, EX.Graph})
+             |> Enum.at(0) == {RDF.iri(EX.S), EX.p(), RDF.iri(EX.O), RDF.iri(EX.Graph)}
+    end
   end
 
   describe "Collectable protocol" do

test/unit/description_test.exs

@@ -953,6 +953,11 @@ defmodule RDF.DescriptionTest do
                  acc |> Description.add(triple)
                end)
     end
+
+    test "Enum.at (for Enumerable.slice/1)" do
+      assert Description.new(EX.S, init: {EX.S, EX.p(), EX.O})
+             |> Enum.at(0) == {RDF.iri(EX.S), EX.p(), RDF.iri(EX.O)}
+    end
   end
 
   describe "Collectable protocol" do

test/unit/graph_test.exs

@@ -1504,6 +1504,11 @@ defmodule RDF.GraphTest do
 
       assert g == Enum.reduce(g, graph(), fn triple, acc -> acc |> Graph.add(triple) end)
     end
+
+    test "Enum.at (for Enumerable.slice/1)" do
+      assert Graph.new({EX.S, EX.p(), EX.O})
+             |> Enum.at(0) == {RDF.iri(EX.S), EX.p(), RDF.iri(EX.O)}
+    end
   end
 
   describe "Collectable protocol" do

test/unit/prefix_map_test.exs

@@ -395,5 +395,9 @@ defmodule RDF.PrefixMapTest do
       assert Enum.reduce(@example2, [], fn mapping, acc -> [mapping | acc] end) ==
                [{:ex2, @ex_ns2}, {:ex1, @ex_ns1}]
     end
+
+    test "Enum.at (for Enumerable.slice/1)" do
+      assert Enum.at(@example2, 0) == {:ex1, @ex_ns1}
+    end
   end
 end

test/unit/property_map_test.exs

@@ -315,5 +315,9 @@ defmodule RDF.PropertyMapTest do
                  {:Baz, RDF.iri(EX.Baz)}
                ]
     end
+
+    test "Enum.at (for Enumerable.slice/1)" do
+      assert Enum.at(@example_property_map, 0) == {:Baz, RDF.iri(EX.Baz)}
+    end
   end
 end