A base-R-only function to check argument inputs to another function, using dots to assess several of those inputs at once

check-type.R

test_fn <- function(x = 1L, y = "x", z = 1.1) {
  .check_type(x, y, z, type = "numeric")
  cat("success")
}

.check_type <- function(..., type = "numeric") {
  
  args <- list(...)
  arg_names <- as.character(substitute(...()))
  names(args) <- arg_names
  
  type_list_lgl <- lapply(args, function(arg) inherits(arg, type))
  
  if (length(failing_args_names) > 0) {
    
    failing_args <- args[names(args) %in% failing_args_names]
    failing_args_classes <- lapply(failing_args, class)
    
    pasted_names <- .make_listed_sentence(names(failing_args_classes))
    pasted_classes <- .make_listed_sentence(failing_args_classes)
    
    stop(
      "The input to argument ", pasted_names, " must be of type ", type, ". " ,
      "You provided input of type ", pasted_classes, ".",
      call. = FALSE
    )
    
  }
  
}

.make_listed_sentence <- function(...) {
  
  values <- c(...)
  
  if (length(values) == 1) {
    return(values)
  }
  
  if (length(values) > 1) {
    last_value <- values[length(values)]
    first_values <- setdiff(values, last_value)
    paste(paste(first_values, collapse = ", "), "and", last_value)
  }
  
}