title: Scala: why can't I map a function accepting Seq[Char] over a collection of Strings
body: <p>I can define a function that accepts a <code>Seq[Char]</code></p>
  
  <pre><code>def f(s: Seq[Char]) = s
  </code></pre>
  
  <p>and it works if I pass in a <code>String</code>:</p>
  
  <pre><code>scala&gt; f("this")
  res8: Seq[Char] = this
  </code></pre>
  
  <p>which means that I can use it in a <code>map</code>:</p>
  
  <pre><code>scala&gt; List("this").map(s =&gt; f(s))
  res9: List[Seq[Char]] = List(this)
  </code></pre>
  
  <p>So why can't I do this?:</p>
  
  <pre><code>scala&gt; List("this").map(f)
  &lt;console&gt;:10: error: type mismatch;
   found   : Seq[Char] =&gt; Seq[Char]
   required: java.lang.String =&gt; ?
                List("this").map(f)
                                 ^
  </code></pre>