I read from here that MIX is not available in releases so code like this wont work in releases

    <%= if Mix.env == :dev do %>
      <a class="title" href="http://<%= post.website.dev_url %>/p/<%= post.id %>-<%= post.slug %>"><img class="card-img-top img-fluid" alt="<%= post.intro %>" src="<%= Application.fetch_env!(:arc, :primary) %><%= WwwSiteCom.Web.Blogs.Post.Image.url(post.filename, :card) %>"></a>
    <% else %>
      <a class="title" href="http://<%= post.website.domain %>/p/<%= post.id %>-<%= post.slug %>"><img class="card-img-top img-fluid" alt="<%= post.intro %>" src="<%= Application.fetch_env!(:arc, :primary) %><%= WwwSiteCom.Web.Blogs.Post.Image.url(post.filename, :card) %>"></a>
    <% end %>

I read a stackoverflow about creating a macro but am wondering if there is any help on offer regarding a EEX example

ideally I want this switching, perhaps I need a function in a view?