gistfile1.rb

class Someclass < Struct.new(:listener)
  def sign_up attributes                                                                             
     post '/sign-up', attributes,                                                                     
         success: ->(response) { listener.user_signed_up attributes.merge(response) },               
         error: ->(cause) {listener.error_signing_up_user cause}                                     
  end
...
end