rlang: Creating empty lists from variable character input

Question

To specify arguments in function created in the args-argument of rlang::new_function, I am looking fora way to create empty lists. These could then be fed into new_function and return functions with predefined arguments.

library(rlang)
create_empty_list <- function(arg_names_chr) {
  # input lenght should be variable, so probably !!! should be used
}

create_empty_list(arg_names_chr = c("arg1", "arg2"))
#> NULL

# desired output
args_specified <- exprs(arg1=, arg2=)
args_specified
#> $arg1
#> 
#> 
#> $arg2

# use with new_function()
new_function(
  args_specified,
  expr(print("hello world")),
  caller_env()
)
#> function (arg1, arg2) 
#> print("hello world")

What I have tried so far:

c("arg1", "arg2") %>% 
  map(parse_expr) %>% 
  exprs(!!!arg_names_chr, .named = TRUE)
#> $arg1
#> arg1
#> 
#> $arg2
#> arg2
#> 
#> # the contents of the list should be empty though... 

I suppose using unquote-splice (!!!) is crucial keep the inputlength flexible, but I couldn't put it together with the empty lists needed for the args-part of new_function yet...

Answer 1

You can create a list the usual way with missing_arg() in it:

arg_names <- c("arg1", "arg2")

args <- rep(list(missing_arg()), length(arg_names))
names(args) <- arg_names

new_function(args, NULL)
#> function (arg1, arg2)
#> NULL