title: Do some replacement in Haskell List Comprehensions
body: <p>My questions is if I put in a string containing such as <code>Hello, today is a Nice Day!!</code> How could I get rid of spaces and punctuation and also replacing the uppercase letters with lowercase?</p>
  
  <p>I know how to delete them but not how to replace them.</p>
  
  <p>Also to get rid of the punctuation.</p>
  
  <p>Sorry I don't know how to mess around with strings, only numbers.</p>
  
  <pre><code>testList xs = [if x = [,|.|?|!] then " "  | x&lt;-xs] 
  </code></pre>