title: What's the difference between include, require and open in OCaml?
body: <p>For example,</p>
  
  <p>include: <code>include Ppx_core</code></p>
  
  <p>open: <code>open Core.Std</code></p>
  
  <p>require: <code>#require "compiler-libs.common"</code></p>
  
  <p>and use: <code>#use "topfind"</code></p>