Range matching in R

range_if.R

range_if = function(.., ..., default = NULL) {
  for (expr in list(...)) {
    s = substitute(expr)
    if (length(s) < 3 || s[[1]] != as.symbol("~")) {
      stop("Invalid argument. Use `condition ~ expression`")
    }
    if (isTRUE(eval(s[[2]]))) return(eval(s[[3]]))
  }
  default
}