R devel - Jul 2013 - On the mechanics of function evaluation and argument matching

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?

Warm Regards,
Brian Rowe


[1]
http://cran.r-project.org/doc/manuals/r-release/R-lang.html#Argument-matching


	[[alternative HTML version deleted]]

On Wed, Jul 17, 2013 at 9:58 AM, Brian Rowe <rowe at 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