title: Smalltalk: how to check wether a string contains only numbers?
body: <p>so basically I have some input possibilities for the user where should only numbers be accepted, otherwise the user will be alerted his input was incorrect.</p>
  
  <p>the input is considered a String when I read it out using a callback.
  now I want to check whether the string(which SHOULD contain numbers) actually DOES ONLY contain numbers, but I didnt find a solution implemented already.
  i tried</p>
  
  <pre><code>theString isInteger 
  </code></pre>
  
  <p>-is never true for the string</p>
  
  <pre><code>theString asNumber 
  </code></pre>
  
  <p>- ignores letters, but I want to have a clear output wether letters are included in the string or not</p>
  
  <pre><code>theString isNumber
  </code></pre>
  
  <p>- always false </p>