title: Scala not found: value mutable
body: <p>I am trying to represent a graph's adjacency list in Scala.</p>
  
  <p>Therefore, I looked at this <a href="https://stackoverflow.com/questions/10358265/representing-a-graph-adjacency-list-with-hashmapint-vectorint-scala">Representing a graph (adjacency list) with HashMap[Int, Vector[Int]] (Scala)?</a> and I tried to represent it as such:</p>
  
  <pre><code>val a = new mutable.HashMap[Int, Vector[Pair[Int, Int]]] withDefaultValue Vector.empty
  </code></pre>
  
  <p>I have imported the following:</p>
  
  <pre><code>import collection.mutable._
  </code></pre>
  
  <p>However, I still get this error:</p>
  
  <pre><code>error: not found: value mutable
  </code></pre>