title: Scheme: how to convert a char to a number/string
body: <p>I am pulling my hair out right now. I am trying to check if a value (which happens to be a char that is the number 5) is a number by comparing it like</p>
  
  <pre><code>(number? (string-&gt;number (list-&gt;string nextchar)))
  </code></pre>
  
  <p>but I keep getting an error of:</p>
  
  <pre><code>list-&gt;string: contract violation
     expected: (listof char?)
    given: #\5
  </code></pre>
  
  <p>How can I convert a char to a number, as well as to a string?</p>