Flexi-add

gistfile1.txt

library(tidyverse)
add <- function(...){
    args <- eval(substitute(alist(...)))
    args <- replaceMissingWithZero(args)
    args %>% purrr::reduce(sum)
}

replaceMissingWithZero <- function(l){
    out <- lapply(l, function(x){
        if (rlang::is_missing(x)) {
                    return(0)
                } else {
                    return(eval(x))
                }
    })
    return(out)
}

add(1, ,3)