Convert an expression to a function

exprToFunction(expr, env = parent.frame(2), quoted = FALSE, caller_offset = 1)


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?
caller_offset If specified, the offset in the callstack of the functiont to be treated as the caller.

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.


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") ## <strong>Not run</strong>: # # Create an output object # output$tripleA <- renderTriple({ # values$A # }) # ## <strong>End(Not run)</strong> # 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"