Flatten a list of tuples in Scala?
<p>I would have thought that a list of tuples could easily be flattened:</p>

<pre><code>scala&gt; val p = "abcde".toList
p: List[Char] = List(a, b, c, d, e)

scala&gt; val q = "pqrst".toList
q: List[Char] = List(p, q, r, s, t)

scala&gt; val pq = p zip q
pq: List[(Char, Char)] = List((a,p), (b,q), (c,r), (d,s), (e,t))

scala&gt; pq.flatten
</code></pre>

<p>But instead, this happens:</p>

<pre><code>&lt;console&gt;:15: error: No implicit view available from (Char, Char) =&gt; scala.collection.GenTraversableOnce[B].
       pq.flatten
          ^
</code></pre>

<p>I can get the job done with:</p>

<pre><code>scala&gt; (for (x &lt;- pq) yield List(x._1, x._2)).flatten
res1: List[Char] = List(a, p, b, q, c, r, d, s, e, t)
</code></pre>

<p>But I'm not understanding the error message.  And my alternative solution seems convoluted and inefficient.</p>

<p>What does that error message mean and why can't I simply flatten a List of tuples?</p>