Thanks for the lead. Given the example in ?missing though, wouldn't it be safer
to explicitly define a default value of NULL:
myplot <- function(x, y=NULL) {
if(is.null(y)) {
y <- x
x <- 1:length(y)
}
plot(x, y)
}
On Jul 17, 2013, at 11:05 AM, "R. Michael Weylandt"
<michael.weyla...@gmail.com> wrote:
> On Wed, Jul 17, 2013 at 9:58 AM, Brian Rowe <r...@muxspace.com> wrote:
>> Hello,
>>
>> Section 4.3.2 of the R language definition [1] states that argument matching
>> to formal arguments is a 3-pass process to match arguments to a function. An
>> error is generated if any (supplied) arguments are left unmatched.
>> Interestingly the opposite is not true as any unmatched formals does not
>> generate an error.
>>
>>> f <- function(x,y,z) x
>>> f(2)
>> [1] 2
>>> f(2,3)
>> [1] 2
>>
>> Since R is lazily evaluated, I understand that it is not an error for an
>> unused argument to be unassigned. However, it is surprising to me that a
>> function need not be called with all its required arguments. I guess in this
>> situation technically "required arguments" means required and referenced
>> arguments.
>>
>>> f()
>> Error in f() : argument "x" is missing, with no default
>>
>> Can anyone shed light on the reasoning for this design choice?
>
> I'm not sure I can, but I'd look around at how the missing() function is used.
>
> Cheers,
> MW
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