closure to automate reactivity functions

server.R

library(shiny)

items <- c("seed")

shinyServer(function(input, output) {

  cl_add_item <- function(name_value, name_button){
    
    # function to add item
    add_item <- reactive({
      
      # register button
      n_click <- input[[name_button]]
      
      if (n_click > 0){
        new_item <- isolate(input[[name_value]]) 
        items <<- c(items, new_item)
      }
      
      return()
      
    })
    
    return(add_item)
    
  }
  
  add_item_a <- cl_add_item("item_add_a", "item_add_a_go")
  add_item_b <- cl_add_item("item_add_b", "item_add_b_go")
      
  get_items <- reactive({
    
    # register "adders"
    add_item_a()
    add_item_b()
    
    return(items)
    
  })

  output$show_items <- renderPrint(get_items())
  
})

ui.R

library(shiny)

shinyUI(pageWithSidebar(
  
  # Application title
  headerPanel("Test of reactivity and closures"),
  
  sidebarPanel(
 
    # add item & go button
    textInput(inputId="item_add_a", label="Add an item here", value=""),
    actionButton(inputId="item_add_a_go", label="Go!"),
    # add item 
    textInput(inputId="item_add_b", label="Or, add an item here", value=""),
    actionButton(inputId="item_add_b_go", label="Go!")
    
  ),
  
  mainPanel(
  
    verbatimTextOutput(outputId="show_items")
    
  )
))