class Sass::Script::Parser

def unary(op, sub)
  class_eval <<RUBY, __FILE__, __LINE__ + 1
    def unary_#{op}
      return #{sub} unless tok = try_tok(:#{op})
      interp = try_op_before_interp(tok)
      return interp if interp
      start_pos = source_position
      node(Tree::UnaryOperation.new(assert_expr(:unary_#{op}), :#{op}), start_pos)
    end
end