Don't fail when creating a rdf:langString literal without a language tag

CHANGELOG.md

@@ -5,6 +5,18 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 [Keep a CHANGELOG](http://keepachangelog.com).
 
 
+## Unreleased
+
+### Changed
+
+- `Literal.new/2` can create `rdf:langString` literals without failing, they are 
+  simply invalid
+
+
+[Compare v0.4.0...HEAD](https://github.com/marcelotto/rdf-ex/compare/v0.4.0...HEAD)
+
+
+
 ## 0.4.0 - 2018-03-10
 
 ### Changed

VERSION

@@ -1 +1 @@
-0.4.0
+0.4.1-dev

lib/rdf/datatypes/lang_string.ex

@@ -10,8 +10,8 @@ defmodule RDF.LangString do
     %Literal{super(value, lexical, opts) | language: String.downcase(language)}
   end
 
-  def build_literal(_, _, _) do
-    raise ArgumentError, "datatype of rdf:langString requires a language"
+  def build_literal(value, lexical, opts) do
+    super(value, lexical, opts)
   end
 
 
@@ -21,5 +21,4 @@ defmodule RDF.LangString do
   def valid?(%Literal{language: nil}), do: false
   def valid?(literal), do: super(literal)
 
-
 end

test/unit/datatypes/lang_string_test.exs

@@ -42,9 +42,10 @@ defmodule RDF.LangStringTest do
       end
     end
 
-    test "without a language it raises an error" do
+    test "without a language it warns and produces an invalid literal" do
       Enum.each @valid, fn {input, _} ->
-        assert_raise ArgumentError, fn -> LangString.new(input) end
+        assert %Literal{} = literal = LangString.new(input)
+        refute Literal.valid?(literal)
       end
     end
   end

test/unit/literal_test.exs

@@ -86,10 +86,9 @@ defmodule RDF.LiteralTest do
       end
     end
 
-    test "construction of a rdf:langString typed literal without language fails" do
-      assert_raise ArgumentError, fn ->
-        Literal.new("Eule", datatype: RDF.langString)
-      end
+    test "construction of a rdf:langString works, but results in an invalid literal" do
+      assert %Literal{value: "Eule"} = literal = Literal.new("Eule", datatype: RDF.langString)
+      refute Literal.valid?(literal)
     end
   end