int foo( int n ,ref  m)
  n
end
-- -- --
s(:list,  [s(:function,  :int, 
  s(:name,  "foo"), 
  s(:parameters, 
    s(:field,  :int,  :n), 
    s(:field,  :ref,  :m)), 
  s(:expressions, 
    s(:name,  "n")))])