My take on immutable models and builders

model.ex

defmodule EasyPeasy
  defrecord Post, 
    id: nil, 
    title: nil, 
    body: nil, 
    publishedOn: nil,
    formatter: nil

  def formatter(post) do 
    "#{post.id} - #{post.title}\n published on #{post.publishedOn}\n\n#{post.body}" 
  end

end

aPost = EasyPeasy.Post.new id: 1, title: "Muahaha", publishedOn: :calendar.local_time, formatter: EasyPeasy.formatter
aPost = aPost.body("Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc eget sagittis eros.")
aPost |> aPost.formatter
aPost = aPost.formatter (fn post -> title)
aPost |> aPost.formatter