title: Haskell - Find and remove element from a list of list
body: <p>I need to find an element l in a list of list, removing each list containing the element, and then return the list of list, but i don't know how to parsing list of list and, at the same time, removing the list and keeping parsing the rest of the list.</p>
  
  <p>To be more understandable, i have : </p>
  
  <pre><code>data Object = Pos Char | Neg Char
       deriving (Show, Eq)
  
  type Box = [Object]
  
  type Formula = [Box]
  
  findAndDelete :: Formula -&gt; Object -&gt; Formula
  findAndDelete cs l
  findAndDelete (c:cs) l
  </code></pre>
  
  <p><strong>edit</strong> : At the same time, I need to remove all x element from the Formula,x is returned by a function named negative with l in parameter.</p>
  
  <pre><code>negative :: Object -&gt; Object
  negative (Pos v) = Neg v
  negative (Neg v) = Pos v
  </code></pre>