def eval data, model = nil
      instance_variable_set :"@model", model
      attributes.each do |name,block|
        instance_variable_set :"@#{name}", instance_eval(&block)
      end

      res = instance_eval &data

      remove_instance_variable :"@model"
      attributes.each do |name,block|
        remove_instance_variable :"@#{name}"
      end

      res
    end
def eval data, model = nil
      instance_variable_set :"@model", model
      attributes.each do |name,block|
        instance_variable_set :"@#{name}", instance_eval(&block)
      end

      res = instance_eval &data

      remove_instance_variable :"@model"
      attributes.each do |name,block|
        remove_instance_variable :"@#{name}"
      end

      res
    end
evaluate data (string or proc) in context of grid