title: haskell, chaining filters
body: <p>to write "map f (map g xs)" as a single call to map you could write</p>
  
  <blockquote>
    <p>example xs = map (f.g) xs</p>
  </blockquote>
  
  <p>but how would you write "filter p (filter q xs)" as a single call to filter? the dot operator doesnt seem to work for filter as it does for maps. guessing you'd use something else for predicates?</p>