title: Strange type of scala "=>:[_, _]"
body: <p>I saw <code>"A =&gt;: A" or "=&gt;:[A, A]"</code> type signature in scalaz.</p>
  
  <p><a href="https://github.com/scalaz/scalaz/blob/scalaz-seven/core/src/main/scala/scalaz/Category.scala" rel="nofollow">https://github.com/scalaz/scalaz/blob/scalaz-seven/core/src/main/scala/scalaz/Category.scala</a></p>
  
  <p>I think this is some kind of scala embedded type but what's this?</p>