rac_keyboard_showing_snippet.rb

keyboard_notification = -> name {
  NSNotificationCenter.defaultCenter.rac_addObserverForName(name, object:nil)
}

rac.showing_keyboard = RACSignal.merge!(
  keyboard_notification.call(UIKeyboardWillShowNotification).map! {|_| true },
  keyboard_notification.call(UIKeyboardWillHideNotification).map! {|_| false}
).takeUntil(self.rac_willDeallocSignal)

rac_signal.rb

class RACSignal
  def self.merge!(*signals)
    self.merge(signals)
  end
end