[Rd] Unexpected interaction between missing() and a blank expression

Hong Ooi hongooi at microsoft.com
Tue Jun 6 18:50:34 CEST 2017

This is something I came across just now:

f <- function(x) missing(x)
z <- quote(expr=)


The object z contains the equivalent of a missing function argument. Another method for generating a missing arg would be alist(a=)$a .

Should f(z) return TRUE in this case? I interpret missing() as checking whether the parent function call had a value supplied for the given argument. Here, I have supplied an argument (z), so I would expect f to return FALSE.

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