title: Ocaml function application operator fails
body: <p>I'm trying to learn ocaml but ran into an issue with the function composition operator |>. </p>
  
  <pre><code>utop # #require "core";;
  utop # open Core;;
  utop # Option.value_exn(Some(1));;
  - : int = 1
  utop # Some(1) |&gt; Option.value_exn;;
  Error: This expression has type
           ?here:Base__Source_code_position0.t -&gt;
           ?error:Base.Error.t -&gt; ?message:string -&gt; 'a option -&gt; 'a
         but an expression was expected of type int option -&gt; 'b
  </code></pre>
  
  <p>I thoght <code>x |&gt; f</code> was supposed to be equivalent to <code>f(x)</code>. Why does <code>Option.value_exn(Some(1))</code> work but not <code>Some(1) |&gt; Option.value_exn</code>?</p>