title: Error in reduceLeft in Map?
body: <p>I'm trying to add key, value pairs in a <code>Map</code> using <code>reduceLeft()</code> but am getting a error. If I add the key value pair using <code>foldleft()</code> I get the right answer. What does this Error mean in <code>reduceLeft</code> and what is the correct code?</p>
  
  <p>Code:</p>
  
  <pre><code>object Dcoder extends App
  {
      var i = Map(1-&gt;2, 3-&gt;4, 5-&gt;6)
      var o = i.reduceLeft((a,b) =&gt; a._1 + b._1)
      println(o)
  }
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>source_file.scala:9: error: type mismatch;
   found   : Int
   required: (Int, Int)
  var o=i.reduceLeft((a,b)=&gt;a._1+b._1)
                            ^
  one error found
  </code></pre>