title: haskell list of tuples, with unique tuples
body: <p>I come from a Python and Java background so Haskell is quite different for me. I'm trying little activities to learn but I am stuck on this .</p>
  
  <p>I have an ordered list of tuples, [(name, studentNumber)], and I want to filter this list so that each student and each studentNumber appears only once. Since the tuples are ordered, I want to keep the first instance of a name or studentNumber and remove any others that may show up.</p>
  
  <p>I tried doing a list comphrenshion, but I'm not sure how to check if a name or number has already been added to the list. </p>