Re: [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 <[EMAIL PROTECTED]>
To:   Spencer Graves <[EMAIL PROTECTED]> 
Cc:   <[EMAIL PROTECTED]>, <[EMAIL PROTECTED]> 
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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