Varying value inside runAction() not changing - swift

Question

I have a run action loop that spawns an enemy then waits and spawns another. The intention is that the higher the score the quicker the enemies spawn.
But the current code has the enemies spawn at the same rate no matter what. I update the rate in the override func update(currentTime: NSTimeInterval) method all the time, so I don't know what's wrong.
override func update(currentTime: NSTimeInterval){
spawnRate = 2.0-(0.1*(Double)(((Double)(Score))/(10.0)))
if(spawnRate < 0.5){
spawnRate = 0.5
}
}
override func didMoveToView(view: SKView) {
runAction(SKAction.repeatActionForever(
SKAction.sequence([
SKAction.runBlock(addEnemy),
SKAction.waitForDuration(spawnRate)
])
))
}

Answer 1

What is happening currently is that you've:
stored duration paramter inside an action
reused that action within sequence over and over again
So nothing actually changes. To solve this, one way would be to use recursive call and change duration parameter each time:
import SpriteKit
class GameScene: SKScene {
let shape = SKSpriteNode(color: UIColor.redColor(), size: CGSize(width: 20, height: 20))
var delay:NSTimeInterval = 1.0
override func didMoveToView(view: SKView) {
recursiveMethod()
}
func recursiveMethod(){
let recursive = SKAction.sequence([
SKAction.waitForDuration(delay),
SKAction.runBlock({self.recursiveMethod();println("delay \(self.delay)")})
])
runAction(recursive)
}
override func update(currentTime: NSTimeInterval) {
if(delay > 0.2){delay = delay - 0.001}
}
}

Answer 2

The problem is that This:
SKAction.sequence([
SKAction.runBlock(addEnemy),
SKAction.waitForDuration(spawnRate)
])
is made one's and then just repeated forever.
try to put the code in a
runAction(SKAction.repeatActionForever(runblock(spawnAndWait()))
and then make a seperate func.
spawnAndWait() { // put here the code for spawning the enemy and waiting spawnrate duration.
b.t.w
Put the code that updates the spawnRate where the score is increased. Because that is more efficient. then in the update method because that is constantly called.