Convert an expression to a function — exprToFunction

exprToFunction(expr, env = parent.frame(), quoted = FALSE)



A quoted or unquoted expression, or a function.


The desired environment for the function. Defaults to the calling environment two steps back.


Is the expression quoted?


This is to be called from another function, because it will attempt to get an unquoted expression from two calls back. Note: as of Shiny 1.6.0, it is recommended to use quoToFunction() instead.


If expr is a quoted expression, then this just converts it to a function. If expr is a function, then this simply returns expr (and prints a deprecation message). If expr was a non-quoted expression from two calls back, then this will quote the original expression and convert it to a function.


# Example of a new renderer, similar to renderText
# This is something that toolkit authors will do
renderTriple <- function(expr, env=parent.frame(), quoted=FALSE) {
  # Convert expr to a function
  func <- shiny::exprToFunction(expr, env, quoted)

  function() {
    value <- func()
    paste(rep(value, 3), collapse=", ")

# Example of using the renderer.
# This is something that app authors will do.
values <- reactiveValues(A="text")

if (FALSE) {
# Create an output object
output$tripleA <- renderTriple({

# At the R console, you can experiment with the renderer using isolate()
tripleA <- renderTriple({

# "text, text, text"