New features

☑️ ..rest args which can be used to name a value for ellipsis arguments.

f <- function(a, b, ..rest) {
  rest
}

Ellipsis arguments are handled a bit different than R already, producing a list of unevaluated closures. The named arguments are no different, allowing them to be operated on as lists, and their values will only be forced when needed.

☑️ Using ..rest arguments in function calls

f(a, b, ..rest)

☑️ Allowing multiple ..rest args

In such cases, the last arg is accepted. This is to allow default values and masking values to be seamlessly combined without having to juggle argument uniqueness between unpacked rest values.

rest <- list(c = 10)
masking_rest <- list(c = 100)

f(a, b, ..rest, ..masking_rest) # equivalent to f(a, b, c = 100)

Future Work

Using ..rest in destructuring assignment

(a, ..rest) <- (1, 2, 3, 4)

Using anonymous .. to disregard additional elements during assignment

(a, ..) <- (1, 2, 3, 4)

Using anonymous .. "more" to partially evaluate a function

sum_nums <- sum(na.rm = TRUE, ..)   # assuming we hold on to the na.rm params... which feels unlikely to me
sum_nums([NA, 1, 2, 3])
# [1] 6