R help - Jun 2013 - Evaluation of function names...

Folks:

Feel free to provide me a link or reference instead of an answer.

Preamble:

f <- function() function(x)rnorm(x)
g <- f()
g(3)
## [1] -0.4448492 -0.2379978 -0.4537394

## But
rnorm <- function()1  ## nasty nasty
g(3)
## Error in rnorm(x) : unused argument(s) (x)

## of course f <- function()function(x)stats:::rnorm(x)
## would fix this.

Question 1:
Suppose I defined f() as at top in a package namespace and exported it.
Would a user see this same error defining g() and with rnorm redefined
as above? (Assume stats is attached as usual).  I presume so, but ...

Question 2:
If the answer to Q1 is yes, (how) can this be avoided without using fully
qualified function names?

Again, a quick reference to relevant docs would suffice.

Thanks.

-- 

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm

On 07/06/2013 14:49, Bert Gunter wrote:
> Folks:
>
> Feel free to provide me a link or reference instead of an answer.
>
> Preamble:
>
> f <- function() function(x)rnorm(x)
> g <- f()
> g(3)
> ## [1] -0.4448492 -0.2379978 -0.4537394
>
> ## But
> rnorm <- function()1  ## nasty nasty
> g(3)
> ## Error in rnorm(x) : unused argument(s) (x)
>
> ## of course f <- function()function(x)stats:::rnorm(x)
> ## would fix this.
>
> Question 1:
> Suppose I defined f() as at top in a package namespace and exported it.
> Would a user see this same error defining g() and with rnorm redefined
> as above? (Assume stats is attached as usual).  I presume so, but ...
Not if done right.  The package should importFrom(stats, rnorm).
> Question 2:
> If the answer to Q1 is yes, (how) can this be avoided without using fully
> qualified function names?
>
> Again, a quick reference to relevant docs would suffice.
'Writing R Extensions' says

'The namespace controls the search strategy for variables used by 
functions in the package. If not found locally, R searches the package 
namespace first, then the imports, then the base namespace and then the 
normal search path.'

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595