Add :base_direction as something supported (or not) by writables.

Author: gkellogg

lib/rdf/mixin/enumerable.rb

@@ -84,6 +84,7 @@ def to_a
     #   * `:validity` allows a concrete Enumerable implementation to indicate that it does or does not support valididty checking. By default implementations are assumed to support validity checking.
     #   * `:skolemize` supports [Skolemization](https://www.w3.org/wiki/BnodeSkolemization) of an `Enumerable`. Implementations supporting this feature must implement a `#skolemize` method, taking a base URI used for minting URIs for BNodes as stable identifiers and a `#deskolemize` method, also taking a base URI used for turning URIs having that prefix back into the same BNodes which were originally skolemized.
     #   * `:quoted_triples` supports RDF 1.2 quoted triples.
+    #   * `:base_direction` supports RDF 1.2 directional language-tagged strings.
     #
     # @param  [Symbol, #to_sym] feature
     # @return [Boolean]

lib/rdf/mixin/writable.rb

@@ -128,7 +128,10 @@ def insert_statements(statements)
       each = statements.respond_to?(:each_statement) ? :each_statement : :each
       statements.__send__(each) do |statement|
         if statement.embedded? && respond_to?(:supports?) && !supports?(:quoted_triples)
-          raise ArgumentError, "Wriable does not support quoted triples"
+          raise ArgumentError, "Writable does not support quoted triples"
+        end
+        if statement.object && statement.object.literal? && statement.object.direction? && !supports?(:base_direction)
+          raise ArgumentError, "Writable does not support directional languaged-tagged strings"
         end
         insert_statement(statement)
       end

lib/rdf/model/graph.rb

@@ -308,6 +308,9 @@ def insert_statement(statement)
       if statement.embedded? && !@data.supports?(:quoted_triples)
         raise ArgumentError, "Graph does not support quoted triples"
       end
+      if statement.object && statement.object.literal? && statement.object.direction? &&  !@data.supports?(:base_direction)
+        raise ArgumentError, "Graph does not support directional languaged-tagged strings"
+      end
       statement = statement.dup
       statement.graph_name = graph_name
       @data.insert(statement)

lib/rdf/repository.rb

@@ -183,6 +183,7 @@ def supports?(feature)
       when :literal_equality then true
       when :atomic_write     then false
       when :quoted_triples   then false
+      when :base_direction   then false
       when :snapshots        then false
       else false
       end
@@ -270,6 +271,7 @@ def supports?(feature)
         when :literal_equality then true
         when :atomic_write     then true
         when :quoted_triples   then true
+        when :base_direction   then true
         when :snapshots        then true
         else false
         end