R lazy evaluation paradox (R bug?) - r

Question

I have multiple functions handing around arguments that may be missing.
e.g. i have
mainfunction <- function(somearg) {
mytest(somearg)
fun <- function() { subfunction(somearg) }
fun()
}
with the interesting aspect that the only interaction of mytest(somearg) with the arg is that it tests if the argument isn’t missing:
mytest = function(somearg) {
print(missing(somearg))
}
subfunction then again tests if it’s missing and treats it accordingly:
subfunction = function(somearg) {
if (missing(somearg))
somearg = NULL
else
somearg = matrix(somearg, cols = 2)
# somearg is used here…
}
the kicker is that, with somearg missing, this doesn’t work: matrix(somearg, cols = 2) throws
argument "somearg" is missing, with no default
during debugging, i found the following:
at the start of mainfunction, missing(somearg) returns TRUE
in mytest, missing(somearg) returns TRUE
insubfunction, missing(somearg) returns FALSE (!!!!)
therefore the matrix branch is hit, but in reality, somearg is missing, so it fails…
wat.

Answer 1

the #BenBolker way:
mainfunction <- function(somearg = NULL) {
mytest(somearg)
fun <- function() { subfunction(somearg) }
fun()
}
mytest = function(somearg) {
print(is.null(somearg))
}
subfunction = function(somearg) {
if (is.null(somearg))
somearg = 1:10
else
somearg = matrix(somearg, ncol = 2)
somearg
}
Another way, using explicit missing argument
mainfunction <- function(somearg) {
is_missing <- missing(somearg)
mytest(is_missing)
fun <- function() { subfunction(somearg, is_missing) }
fun()
}
mytest = function(x) { print(x) }
subfunction = function(somearg, is_arg_missing) {
if (is_arg_missing)
somearg = 1:10
else
somearg = matrix(somearg, ncol = 2)
somearg
}
A third way, using plain missing arg passing:
mainfunction <- function(somearg) {
is_missing <- missing(somearg)
mytest(somearg)
fun <- function() {
if (is_missing) subfunction() else
subfunction(somearg)
}
fun()
}
mytest = function(somearg) {
print(missing(somearg))
}
subfunction = function(somearg) {
if (missing(somearg))
somearg = 1:10
else
somearg = matrix(somearg, ncol = 2)
somearg
}