title: Haskell filter function on strings
body: <p>Is there a way to use the filter function on Strings, this way:</p>
  
  <pre><code>filter (=="!") "!!some!!_!!string!!"
  </code></pre>
  
  <p>should output <code>"some_string"</code> (case above). Right now all i get is a type error:</p>
  
  <pre><code>Couldn't match expected type `[Char]' against inferred type `Char'
  </code></pre>
  
  <p>If i change the second filter argument type to ["!!some!!_!!string!!"], the type error disappears, yet only an empty list is outputted. (Not exactly what i want)</p>
  
  <p>I thought that strings were lists but obviously "!!some!!_!!string!!" isn't regarded as a list but as a char.</p>
  
  <p>Any hints someone ? </p>