[R] Summary: do.call and environments

[Spencer Graves]

      I got the following from S-Plus 6.2: 

 > x <- 7
 > fx <- function(y)
print(x * y)
 > f <- function(fx, x)
do.call(fx, list(3))
 > f("fx", 2)
[1] 21
[1] 21

      This is the same as R 1.8.1 except for that S-Plus printed the 
result in addition to returning it. 

      Thanks,
      Spencer Graves

Gabor Grothendieck wrote:

>Note that R and S are fundamentally different when it comes to
>scoping.  
>
>R uses lexical scoping, i.e. the parent environment of a function
>is the environment at the point where it is *defined* whereas
>S uses dynamic scoping, i.e. the parent environment in a function 
>is the environment at the point where the function is *called*.
>
>Thus, anything regarding scoping will be different in the 
>two systems.
>
>Note that in S, the question is easy since all you need is:
>
>x <- 7
>fx <- function(y) print(x*y)
>f <- function(fx, x) do.call(fx,list(3))
>f("fx",2)
>
>This gives 6 in S but 21 in R.  (Better check this since I
>don't have access to S and am going by my understanding.)
>
>In fact, this entire exercise can be regarded as simulating
>S-style dynamic scoping in R.
>
>---
>Date:   Thu, 11 Mar 2004 09:45:32 +0100 
>From:   Thomas Petzoldt <petzoldt at rcs.urz.tu-dresden.de>
>To:   Spencer Graves <spencer.graves at pdf.com> 
>Cc:   <ggrothendieck at myway.com>, <r-help at stat.math.ethz.ch> 
>Subject:   Re: [R] Summary: do.call and environments 
>
> 
>Hello,
>
>  
>
>>>f("fx",2)
>>>      
>>>
>>[1] 6
>>
>>I would have naively expected 14. From whence cometh "6"?
>>Also, I prefer to use transportable code wherever feasible. The 
>>    
>>
>
>2*3=6, which was the intention. It is in fact only a proof of 
>correctness, that "7" is not used here. The proposal of Gabor does 
>exactly, what I want, but if it does not work on S-PLUS, it's a serious 
>disadvantage and I should check this too.
>
>Thomas P.
>
>
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