int foo(ref x)
  a = 5
end

foo( 3 )
-- -- --
s(:expressions,
  s(:function, :int,
    s(:name, :foo),
    s(:parameters,
      s(:parameter, :ref, :x)),
    s(:expressions,
      s(:assign,
        s(:name, :a),
        s(:int, 5)))),
  s(:call,
    s(:name, :foo),
    s(:arguments,
      s(:int, 3))))