Example of formals-aware decorator

match_to_formals.R

is.unset<-function(x)
  x==as.list(alist(a=))[[1]]

is.nameempty <- function(x){
  nx <- names(x)
  if(is.null(nx))
    return(rep(TRUE, length(x)))
  is.na(nx) | nx==""
}

match_to_formals <- function(a, f, keep_passed_names=TRUE){
  l_wo_names <- is.nameempty(a)
  # named arguments only
  a_w_names <- names(a)[!l_wo_names]
  # how many arguments are unnamed
  l_unn <- length(a[l_wo_names])
  # formals, which have not been explicitly referred to in arguments
  nms_f <- names(f)[!names(f) %in% a_w_names]
  # position of dots in unreferred formals, if not found, assumed to be at the end
  dots_pos <- match("...", nms_f, nomatch = length(nms_f)+1)
  # foreign names (names passed to dots) can be suppressed, but it is probably not a good idea
  if(!keep_passed_names){
    a_w_names <- ifelse(a_w_names %in% names(f), a_w_names, "...")
    names(a)[!l_wo_names] <- a_w_names # this part has names so it is matched literally
  }
  
  names(a)[l_wo_names] <- c(nms_f[seq_len(min(l_unn, dots_pos-1))],             # this part is matched by position
                            rep.int("...", times=max(0,l_unn-dots_pos+1)))  # this part is passed to dots
  a
}


myfun <- function(a,..., b=1, NArm=TRUE){
  (a-b*sum(..., na.rm=NArm))
}

consciously <- function(fun, x){
  f_formals <- formals(args(fun))
  function(...){
    arg_lst <- list(...)
    af <- match_to_formals(arg_lst, f_formals)
    message("Here's what I got:")
    message(str(af))
    fun(...)
    #do.call(fun, af) # if you want to modify arguments
  }
}

conscious_myfun <- consciously(myfun)

conscious_myfun(1:3, 1:3, k=5:7, b=0.4)
#> Here's what I got:
#> List of 4
#>  $ a  : int [1:3] 1 2 3
#>  $ ...: int [1:3] 1 2 3
#>  $ k  : int [1:3] 5 6 7
#>  $ b  : num 0.4
#> 
#> [1] -8.6 -7.6 -6.6


#<sup>Created on 2020-06-08 by the [reprex package](https://reprex.tidyverse.org) (v0.3.0)</sup>