title: Destructure a List of Pairs
body: <p>Consider</p>
  
  <pre><code>.say for (1,2,2).rotor(2=&gt;-1).map( -&gt; ($a, $b) { $a - $b })
  </code></pre>
  
  <p>which works as expected. However,</p>
  
  <pre><code>.say for (1,2,2).pairs.rotor(2=&gt;-1).map( -&gt; ($a, $b) { $a.value - $b.value })
  </code></pre>
  
  <p>throws </p>
  
  <pre><code>Too few positionals passed to '&lt;anon&gt;'; expected 2 arguments but got 0 in sub-signature
  </code></pre>
  
  <p>Is this a bug or am I missing something?</p>
  
  <blockquote>
    <p>This is Rakudo Star version 2019.03.1 built on MoarVM version 2019.03
    implementing Perl 6.d.</p>
  </blockquote>