title: Split a String by a String
body: <p>I'm trying to construct a lexer analyzer using Haskell and I need to construct a function <code>f :: String -&gt; String -&gt; (String, String)</code> which split the input in a tuple of strings. The function need to split by a known String. The known String is always at the start of the String to be parsed.</p>
  
  <p>For example if the String to split is "expression" and the input is "expression rest of String" I need to generate an output ("expression", "rest of String").</p>
  
  <p>I'm trying to avoid using advanced libraries.</p>
  
  <p>Any help?</p>
  
  <p>Thanks.</p>