A neat thing you can do with Intermodal + functional Ruby

some_api.rb

require 'rlet/functional'

module SomeApi
  module API
    class V1_0 < Intermodal::API
      using RLet::Functional

      self.default_per_page = 25

      map_data do
        attribute = ->(field) { ->(r) { r.send(field) } }
        helper    = ->(_method) { ActionController::Base.helpers.method(_method) }

        presentation_for :book do
          presents :id
          presents :price,    with: attribute.(:price) | helper.(:number_to_currency)
        end
      end
    end
  end
end

@brandondees to expand further on what I mean by "flexible", the | is an applicative operator. That means you can chain functions along the lines of:

presents :price, with: attribute.(:price) | locale.(:fr) | helper.(:number_to_currency)

as an example.