title: Higher order iterators in Ruby?
body: <p>I was reading a Ruby question about the <code>.each</code> iterator, and someone stated that using <code>.each</code> can be a code smell if higher order iterators are better suited for the task. What are higher order iterators in Ruby?</p>
  
  <p><strong>edit:</strong> Jörg W Mittag, the author of the StackOverflow answer that I was referring to mentioned that he meant to write higher <em>level</em> iterators, but he also explained what they are very well below.</p>