add/remove shapefile layer on checkbox in leaflet map

I have a shiny application where I have a leaflet-map and checkboxes.

What I want to do is the following.

I want to render a shapefile when a checkbox is checked and remove it when the checkbox gets unchecked.

ui.R

library(shiny)
library(leaflet)
# Define UI for application that draws a histogram
shinyUI(
  fluidPage(
    leafletOutput("mymap"),
    checkboxInput(inputId = "direction",
                  label = strong("Traffic Directions"),
                  value = FALSE),
    checkboxInput(inputId = "madrid",
                  label = strong("Madrid Outlines"),
                  value = FALSE)
  )
)

server.R

library(shiny)
library(rgdal)

shinyServer(function(input, output, session) {
  ##SHAPEFILES
  madridShape <- readOGR("./madridshapefile/", "Distritos")
  directions <- readOGR("./directions/", "directions")

  output$mymap <- renderLeaflet({
    leaflet() %>%
      addProviderTiles(providers$CartoDB.Positron,
                       options = providerTileOptions(noWrap = )
      ) %>%
      setView(lng = -3.8196207,
              lat = 40.4678698,
              zoom = 10)
  })

})

What do I have to do in order to achieve my goal?

I tried something like this for when the checkbox gets checked :

if (input$direction == true){
  output$mymap <- addPolygons(data=madridShape,weight=1,col = 'black') %>% 
}

I seem to miss something though because it's not working.