print the content of returned reactive expression from module

[Pweide]

Hi there,
I'm new to Shiny and still try to wrap my head around modules and how to return reactive expressions from there. I would like to be able to follow the changes of a reactive expression based on user input. Therefore, I would like to use a simple print function to output the content of a given expression to the console, but I fail to do so. I found a way to do it with reactive values but this doesn't work for reactive expressions. If I simply try to use print(ret()$mut) in the main app I get following error:
Error in ret() : could not find function "ret"
Here is a minimal example:

library(shiny)

##### Module UI function #####
cellLineSelectorUI <- function(id){
  # create a namespace function using the provided id
  ns <- NS(id)
  
  tagList(
    mainPanel(
      titlePanel("Interactive Cell line selector"),
      tabsetPanel(
        tabPanel("Simple Selection / Gene expression based",
                 sidebarLayout(
                   sidebarPanel(radioButtons(inputId = ns("project"), #name of input
                                             label = "Project:", #label displayed in ui
                                             choices = as.character(c("abc", "cdf")),
                                             selected = "abc") #default choice (not required)
                   ),
                   mainPanel(
                     verbatimTextOutput(ns("mutation"))
                   )
                 )
        )
      )
    )
  )
}

##### Module server function #####
cellLineSelector <- function(input, output, session) {
  
  # restrict the choices of available mutations based on the cell lines with available gene expression data in the selected project
  mutations <- reactive({
    # check if input is specified - if not stop executing the rest of this code block
    req(input$project)
    
    if (input$project== 'abc') {
        mutation_list <- rep("a",10)
      
    }
    else{ 
        mutation_list <- rep("d",10)
    }
    return(list("mutation_list"=mutation_list))
  })
  ### I want to follow the changes of mutations()$mutation_list
  ### as a workaround I can output it directly to the app but I want to just print the content to the console
  output$mutation <- renderText({
    mutations()$mutation_list
  })
  
  return(list(mut=mutations)  
  )
}
##### Main app #####
ui <- fluidPage(title="Test",
  cellLineSelectorUI("test")
                
)
server <- function(input, output, session) {
  ret <- callModule(cellLineSelector, "test")
  ### How can I now print the value of ret()$mut ?
  print(ret()$mut)
}

shinyApp(ui = ui, server = server)

[Pweide]

I found a solution now. Wrap the print in an observe function:

server <- function(input, output, session) {
  ret <- callModule(cellLineSelector, "test")
  ### How can I now print the value of ret()$mut ?
  observe(print(ret$mut()$mutation_list))
}