Defining success for a no-variable query as returning [{}], all special

casing for variable count can be removed.

lib/rdf/query.rb

@@ -192,46 +192,37 @@ def optimize!(options = {})
     # @see    http://www.holygoat.co.uk/blog/entry/2005-10-25-1
     def execute(queryable, options = {})
       @solutions = Solutions.new
-      @failed = false
       @patterns.each do |pattern|
-        case pattern.variable_count
-          when 0 # no variables
-            if pattern.execute(queryable).empty?
-              # return an empty solution sequence:
-              @solutions.clear
-              @failed = true
-              break
-            end
-
-          else case # 1 or 2 variables
+        case # 1 or 2 variables
 
-            when !@solutions.have_variables?(pattern.variables.values)
-              if @solutions.empty?
-                pattern.execute(queryable) do |statement|
-                  @solutions << pattern.solution(statement)
-                end
-              else # union
-                old_solutions, @solutions = @solutions, Solutions.new
-                pattern.execute(queryable) do |statement|
-                  old_solutions.each do |solution|
-                    @solutions << solution.merge(pattern.solution(statement))
-                  end
-                end
+          when !@solutions.have_variables?(pattern.variables.values)
+            if @solutions.empty?
+              pattern.execute(queryable) do |statement|
+                @solutions << pattern.solution(statement)
               end
-
-            else # also union
+            else # union
               old_solutions, @solutions = @solutions, Solutions.new
-              old_solutions.each_with_index do |solution, index|
-                pattern.execute(queryable, solution) do |statement|
+              pattern.execute(queryable) do |statement|
+                old_solutions.each do |solution|
                   @solutions << solution.merge(pattern.solution(statement))
                 end
               end
-          end
+            end
+
+          else # also union
+            old_solutions, @solutions = @solutions, Solutions.new
+            old_solutions.each_with_index do |solution, index|
+              pattern.execute(queryable, solution) do |statement|
+                @solutions << solution.merge(pattern.solution(statement))
+              end
+            end
         end
+        # It's important to abort failed queries quickly because later patterns
+        # that can have constraints are often broad without them.
+        # We have no solutions at all:
+        return @solutions if @solutions.empty?
+        # We have no solutions for variables we should have solutions for:
         if !pattern.optional? && pattern.variables.keys.any? { |variable| !@solutions.variable_names.include?(variable) }
-          # no point continuing, there are no bindings.  It's important to
-          # abort because later patterns that can have constraints are often
-          # broad without them.
           return Solutions.new
         end
       end