title: What does :: (double colon) mean in Ocaml?
body: <p>formal_list: typ ID { [($1,$2)] }
  | formal_list COMMA typ ID { ($3,$4) :: $1 }</p>
  
  <p>What does the <code>::</code> operator mean?
  For instance: <code>a :: b</code>
  Is the meaning that we add a to b?</p>