ios - How to use runAction syntax correctly for the following -

i'm trying following

//increase spaceship frequency     self.runaction(skaction.repeatactionforever(skaction.waitforduration(1), completion: {          difficulty -= 0.01         println("difficulty increased")      })) 

basically need skaction.waitforduration(1) completion run forever tried wrap around runaction

i following error: "extra argument 'completion' in call"

if want use spritekit, use action sequence:

self.runaction(skaction.repeatactionforever(skaction.sequence([skaction.waitforduration(1), skaction.runblock({     difficulty -= 0.01;     println("difficulty increased"); })]))); 

but, should using nstimer.