class Sass::Script::UnaryOperation

def to_sass(opts = {})

Other tags:
    See: Node#to_sass - 
def to_sass(opts = {})
  operand = @operand.to_sass(opts)
  if @operand.is_a?(Operation) ||
      (@operator == :minus &&
       (operand =~ Sass::SCSS::RX::IDENT) == 0)
    operand = "(#{@operand.to_sass(opts)})"
  end
  op = Lexer::OPERATORS_REVERSE[@operator]
  op + (op =~ /[a-z]/ ? " " : "") + operand
end