String & expression

expr.R

library(shiny)

string <- "print('from string')"
installExprFunction({print("from expression")}, "expr")

ui <- fluidPage(
  verbatimTextOutput("string"),
  verbatimTextOutput("expression")
)

server <- function(input, output, session){
  output$string <- renderPrint({eval(parse(text = string))})
  output$expression <- renderPrint({expr()})
}

shinyApp(ui, server)

module.R

library(shiny)

expr <- quote(rnorm(1000))

plot_ui <- function(id){
	ns <- NS(id)
	plotOutput(ns("plot"))
}

plot <- function(input, output, session, expr){
	output$plot <- renderPlot({hist(eval(expr))})
}

ui <- fluidPage(
	plot_ui("mod")
)

server <- function(input, output, session){
	callModule(plot, "mod", expr = expr)
}

shinyApp(ui, server)

wrapper.R

library(shiny)

expr <- quote(rnorm(100))

myFunc <- function(expr){

	ui <- fluidPage(
		plotOutput("plot")
	)

	server <- function(input, output, session){
		output$plot <- renderPlot({
			hist(
				eval(expr)
			)
		})
	}

	shinyApp(ui, server)
}

myFunc(expr)

With the wrapper I could do:

library(shiny)
expr <- quote(
  output$plot <- renderPlot({
    hist(rnorm(input$obs))
  })
)
myFunc <- function(expr){
  ui <- fluidPage(
    sliderInput(
      "obs", 
      "Number of observations:",
      min = 0, 
      max = 1000, 
      value = 500
    ),
    plotOutput("plot")
  )
  server <- function(input, output, session){
    eval(expr)
  }
  shinyApp(ui, server)
}
myFunc(expr)

I have to see if modules are a cleaner way to do that and what is the impact on user-friendliness