def _perform(environment)
literal1 = @operand1.perform(environment)
literal2 = @operand2.perform(environment)
if @operator == :concat && context == :equals
literal1 = Sass::Script::String.new(literal1.value) if literal1.is_a?(Sass::Script::String)
literal2 = Sass::Script::String.new(literal2.value) if literal2.is_a?(Sass::Script::String)
end
begin
opts(literal1.send(@operator, literal2))
rescue NoMethodError => e
raise e unless e.name.to_s == @operator.to_s
raise Sass::SyntaxError.new("Undefined operation: \"#{literal1} #{@operator} #{literal2}\".")
end
end