Shiny R - Re-initialise reactive values

server.r

library(shiny)

shinyServer(function(input,output){
  reval <- reactiveValues(a= 1,b=2,dummy= rnorm(1))
  
  observe({
    if(input$hello == 0) return()    
    random.number <-  rnorm(1)
    reval$dummy <-  random.number
    b <- reval$b
    reval <<- reactiveValues(a = 1,b = b + 1,dummy=random.number)        
  })
  
  output$a <- renderUI({
    reval$dummy
    HTML(reval$b)
  })
})

ui.r

library(shiny)
shinyUI(basicPage(
    actionButton("hello","Increase Reactive Value"),
    htmlOutput("a"),
    HTML('<script src="https://gist.github.com/xiaodaigh/6946423.js"></script>')
  )
)