Convert an expression to a function

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.

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

Arguments

expr	A quoted or unquoted expression, or a function.
env	The desired environment for the function. Defaults to the calling environment two steps back.
quoted	Is the expression quoted?

Details

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.

Examples

# 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$tripleA <- renderTriple({
  values$A
})
}

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

isolate(tripleA())
#> [1] "text, text, text"
# "text, text, text"