# File lib/arel/algebra/relations/operations/join.rb, line 60
    def eval
      result = []
      relation1.call.each do |row1|
        relation2.call.each do |row2|
          combined_row = row1.combine(row2, self)
          if predicates.all? { |p| p.eval(combined_row) }
            result << combined_row
          end
        end
      end
      result
    end