r - How to avoid promise already under evaluation warning for setting default argument as a function of another argument -

i've read other answers issues related "promise under evaluation" warning, unable see how can me avoid problem.

here have function 1 method, takes default argument value function of value.

myfun <- function(x, ones = null) {     usemethod("myfun") }   myfun.list <- function(x, ones = na) {     data.frame(x = x[[1]], ones) }  ones <- function(x) {     rep(1, length(x)) } 

so far, good:

myfun(list(letters[1:5])) ##   x ones ## 1   na ## 2 b   na ## 3 c   na ## 4 d   na ## 5 e   na 

but when define method sets default ones argument function ones(x), error:

myfun.character <- function(x, ones = ones(x)) {     myfun(as.list(x), ones) }  myfun(letters[1:5]) ## error in data.frame(x = x[[1]], ones) :  ##  promise under evaluation: recursive default argument reference or earlier problems?  

for various reasons, need keep argument name same function name (for ones). how can force evaluation of argument within my fun.character? need work (which does):

myfun(letters[1:5], 1:5) ##   x ones ## 1    1 ## 2    2 ## 3    3 ## 4    4 ## 5    5 

thanks!

one need deep r's (notorious) environments understand exactly, tries find ones. problem located in way supplied , default arguments evaluated within function. can see this link r manual , explanation here.

the easy solution tell r it. save hassle. in case that's global environment.

changing method myfun.character tell ones in global environment:

myfun.character <- function(x, ones = get('ones', envir = globalenv())(x)) {    myfun(as.list(x), ones)  } 

will enough here.

out:

myfun(letters[1:5]) #  x ones #1    1 #2    1 #3    1 #4    1 #5    1  myfun(letters[1:5], 1:5) #  x ones #1    1 #2    2 #3    3 #4    4 #5    5