Add top-level functions for the two boolean RDF.Literal values

CHANGELOG.md

@@ -10,6 +10,8 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 ### Added
 
 - top-level alias functions for constructors of the basic datatypes
+- top-level constant functions `RDF.true` and `RDF.false` for the two boolean 
+  RDF.Literal values
 
 
 [Compare v0.4.1...HEAD](https://github.com/marcelotto/rdf-ex/compare/v0.4.1...HEAD)

lib/rdf.ex

@@ -151,6 +151,9 @@ defmodule RDF do
     defdelegate unquote(term)(s, o1, o2, o3, o4, o5), to: RDF.NS.RDF
   end
 
+  defdelegate unquote(:true)(),  to: RDF.Boolean.Value
+  defdelegate unquote(:false)(), to: RDF.Boolean.Value
+
   defdelegate langString(),   to: RDF.NS.RDF
   defdelegate unquote(nil)(), to: RDF.NS.RDF
 

lib/rdf/datatypes/boolean.ex

@@ -25,3 +25,18 @@ defmodule RDF.Boolean do
   def convert(value, opts), do: super(value, opts)
 
 end
+
+defmodule RDF.Boolean.Value do
+  @moduledoc false
+
+  # This module holds the two boolean value literals, so they can be accessed
+  # directly without needing to construct them every time. They can't
+  # be defined in the RDF.Boolean module, because we can not use the
+  # `RDF.Boolean.new` function without having it compiled first.
+
+  @xsd_true  RDF.Boolean.new(true)
+  @xsd_false RDF.Boolean.new(false)
+
+  def unquote(:true)(),  do: @xsd_true
+  def unquote(:false)(), do: @xsd_false
+end

test/unit/rdf_test.exs

@@ -11,4 +11,8 @@ defmodule RDFTest do
        end)
   end
 
+  test "true and false aliases" do
+    assert RDF.true  == RDF.Boolean.new(true)
+    assert RDF.false == RDF.Boolean.new(false)
+  end
 end