R help - May 2011 - change function scope?

I'm still getting used to R's scoping. I've run into the following
situation

value=0
thefunction <- function() print( value )
somefunction <- function() { value=99; thefunction() }
somefunction()

now, I understand that somefunction() returns 0 because thefunction() was
defined with value=0 in its parent envrionment, it dosent look at all in the
environment of somefunction. My question is can I re-scope thefunction in
the somefunction environment?? (So that somefunction() returns 99). I've
tried various uses of eval() and assign() with their keywords in the
definition of somefunction and have had no luck at all.

I do see that i could define thefunction in some external file and source it
inside somefunction, but that seems clumsy.

thanks!!

James

	[[alternative HTML version deleted]]

Thanks to Mark for an off-list suggestion which works.

somefunction <- function() { value=99; environment(thefunction) <-
environment(); thefunction() }

this apparently defines a copy of thefunction within somefunction, exactly
what I wanted. thefunction in the global env is unchanged.

It seems so obvious, but it would have been alot more head scratching. The
help is very much appreciated!

James

On Thu, May 26, 2011 at 3:09 PM, James McCreight
<jlmccreight@gmail.com>wrote:
> I'm still getting used to R's scoping. I've run into the
following
> situation
>
> value=0
> thefunction <- function() print( value )
> somefunction <- function() { value=99; thefunction() }
> somefunction()
>
> now, I understand that somefunction() returns 0 because thefunction() was
> defined with value=0 in its parent envrionment, it dosent look at all in
the
> environment of somefunction. My question is can I re-scope thefunction in
> the somefunction environment?? (So that somefunction() returns 99).
I've
> tried various uses of eval() and assign() with their keywords in the
> definition of somefunction and have had no luck at all.
>
> I do see that i could define thefunction in some external file and source
> it inside somefunction, but that seems clumsy.
>
> thanks!!
>
> James
>
	[[alternative HTML version deleted]]

On Thu, May 26, 2011 at 5:09 PM, James McCreight <jlmccreight at
gmail.com> wrote:
> I'm still getting used to R's scoping. I've run into the
following situation
>
> value=0
> thefunction <- function() print( value )
> somefunction <- function() { value=99; thefunction() }
> somefunction()
>
> now, I understand that somefunction() returns 0 because thefunction() was
> defined with value=0 in its parent envrionment, it dosent look at all in
the
> environment of somefunction. My question is can I re-scope thefunction in
> the somefunction environment?? (So that somefunction() returns 99).
I've
> tried various uses of eval() and assign() with their keywords in the
> definition of somefunction and have had no luck at all.
>
> I do see that i could define thefunction in some external file and source
it
> inside somefunction, but that seems clumsy.
>
Aside from explicitly setting the environment of thefunction, note
that this sort of thing is often an attempt to do OO programming
without realizing it.  With the proto package you could make this
explicit.  Here p is a proto object with property value and methods
thefunction and somefunction:

library(proto)
value <- 0
p <- proto(value = 99,
  thefunction = function(this) print(this$value),
  somefunction = function(this) this$thefunction()
)
p$somefunction() # 99

# we can also change the value property:

p$value <- 100
p$somefunction() # 100

# or create a child with its own value such that p delegates the two
methods to child but child overrides p's value with its own.

child <- p$proto(value = 3)
child$somefunction() # 3
p$somefunction() # still 100


-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com

On 11-05-26 5:09 PM, James McCreight wrote:
> I'm still getting used to R's scoping. I've run into the
following situation
>
> value=0
> thefunction<- function() print( value )
> somefunction<- function() { value=99; thefunction() }
> somefunction()
>
> now, I understand that somefunction() returns 0 because thefunction() was
> defined with value=0 in its parent envrionment, it dosent look at all in
the
> environment of somefunction. My question is can I re-scope thefunction in
> the somefunction environment?? (So that somefunction() returns 99).
I've
> tried various uses of eval() and assign() with their keywords in the
> definition of somefunction and have had no luck at all.
>
> I do see that i could define thefunction in some external file and source
it
> inside somefunction, but that seems clumsy.
>
Yes, you've been told how to do it:  but you almost certainly shouldn't.
  Think of functions as functions, not as macros.  Changing the 
environment of a function is like editing it.  Would you ask how to 
change the body of thefunction from within somefunction?  You can in R, 
but you shouldn't.

Duncan Murdoch