title: Error function_clause?
body: <p>Why is this not working? Can't figure this out. Seems to be something with the way strings are matched.
  I keep getting an error <code>error:function_clause</code>.</p>
  
  <pre><code>-module(rna_transcription).
  -export([to_rna/1, to_rna_nucleotide/1]).
  
  to_rna(DNA) -&gt; lists:map(fun to_rna_nucleotide/1, DNA).
  
  to_rna_nucleotide("G") -&gt; "C";
  to_rna_nucleotide("C") -&gt; "G";
  to_rna_nucleotide("T") -&gt; "A";
  to_rna_nucleotide("A") -&gt; "U".
  </code></pre>