R function to validate the input from readline

readline_check

#' Check readline input
#'
#' @param prompt the prompt for readline
#' @param type what type of check to perform, one of c("numeric", "character", "length", "minlength", "maxlength", "exact", "grep")
#' @param compare the comparator for exact and (min|max)length types
#' @param ... other arguments to pass to grep
#'
#' @return the validated result of readline
#' @export
#'
#' @examples
#' readline_check("Type a number: ", "numeric")
#' readline_check("Type two characters: ", "length", 2)
#' readline_check("Type at least 3 characters: ", "minlength", 3)
#' readline_check("Type no more than 4 characters: ", "maxlength", 4)
#' readline_check("Type a letter and a number: ", "grep", pattern = "^[a-zA-Z]\\d$")
#' 
readline_check <- function(prompt, type = c("numeric", "length", "minlength", "maxlength", "exact", "grep"), compare = NULL, ...) {
  input <- readline(prompt)
  if (type == "numeric") {
    check <- suppressWarnings(!is.na(as.numeric(input)))
  } else if (type == "exact") {
    check <- input == compare
  } else if (type == "length") {
    check <- nchar(input) == compare
  } else if (type == "minlength") {
      check <- nchar(input) >= compare
  } else if (type == "maxlength") {
    check <- nchar(input) <= compare
  } else if (type == "grep") {
    check <- grep(x = input, ...) %>% length() > 0
  } else {
    check <- FALSE # default false if type is wrong?
  }
  if (!check) {
    readline_check(prompt, type[1], compare, ...)
  } else {
    input
  }
}


n <- readline_check("Type a number: ", "numeric")
yes <- readline_check("Type 'yes': ", "exact", "yes")
c2 <- readline_check("Type two characters: ", "length", 2)
c3 <- readline_check("Type at least 3 characters: ", "minlength", 3)
c4 <- readline_check("Type no more than 4 characters: ", "maxlength", 4)
ln <- readline_check("Type a letter and a number: ", "grep", pattern = "^[a-zA-Z]\\d$")