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

I don't always like having English-like DSL for everything. Data transformation tends to be one of them.

presents :price, taken_from attribute.(:price), via helper.(:number_to_currency)

is just too wordy for what is essentially a data transformation. More importantly, it's not likely to be as flexible.

Elixir is a syntax that takes what made Ruby look good and built it on top of the Erlang BEAM VM. So it's functional in that sense, but Elixir's sweet spot is that it has better metaprogramming than Erlang itself while retaining what makes Erlang capable for the problems it solves well. Many of Elixir's basic syntax and sugar are actually Lisp-style macro expansions, so it's a bit different from Ruby-style metaprogramming.

@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.