Custom tab completion in R function

Question

I am currently writing a function which only accepts certain inputs (in the example only "a" and "b"). For all other inputs the function will return an error.

test <- function(x) {
  allowedX <- c("a","b")
  if(x %in% allowedX) print("Good choice!")
  else stop("wrong input!")
}

To help users of the function I would like to supply the allowed values for x (stored in allowedX) using the tab completion feature in R and replace the default file name completion which is typically applied after a quote. So pressing TAB should give something like:

test(x="<TAB>
a b

However, I couldn't find a solution so far how to map the vector allowedX to the tab completion in R. Can somebody tell me how to do that?

Thanks in advance!

Answer 1

You could try something like the following:

test <- function() {
  allowedX <- c("a","b")
  x = readline('Please enter your choice of parameters (either "a" or "b"): ')
  if(x %in% allowedX) print("Good choice!")
  else stop("wrong input!")
}