title: 2 FoldLefts are Equal
body: <p>Why do both of the following <code>foldLeft</code>'s result in the same output?</p>
  
  <p><strong>#1</strong></p>
  
  <pre><code>scala&gt; List(1,2,3).foldLeft(List[Int]())( (acc, el) =&gt; acc :+ el)
  res114: List[Int] = List(1, 2, 3)
  </code></pre>
  
  <p>And, now using <code>_ :+ _</code> as the <code>(B, A) =&gt; B</code> argument.</p>
  
  <p><strong>#2</strong></p>
  
  <pre><code>scala&gt; List(1,2,3).foldLeft(List[Int]())(_ :+ _)
  res115: List[Int] = List(1, 2, 3)
  </code></pre>
  
  <p>In particular, the lack of explicitly appending to the <code>accumulator</code> in the second case confuses me.</p>