R help - Mar 2010 - passing a function as an argument using lazy loading

I have the following function that makes use of lazy loading.

foo <- function(x=2*y, y=x/2) cat(x,y)

Now I want to be able to modify it like below:

foo(y=x/3)

Of course, this does not work as the object x is not known. Still I  
would like to be able to pass a function as an argument that is  
evaluated using lazy loading.

Can someone help?

Thanks,
Mark
???????????????????????????????????????
Mark Heckmann
Dipl. Wirt.-Ing. cand. Psych.
Vorstra?e 93 B01
28359 Bremen
Blog: www.markheckmann.de
R-Blog: http://ryouready.wordpress.com

On 10.03.2010 13:26, Mark Heckmann wrote:
> I have the following function that makes use of lazy loading.

I guess you mean *lazy evaluation* rather than *lazy loading* (as used 
in loading functions or data from the package databases).

> foo <- function(x=2*y, y=x/2) cat(x,y)
>
> Now I want to be able to modify it like below:
>
> foo(y=x/3)

You really want to *modify* the list of formal arguments like that or do 
you want to *call* it like that?

> Of course, this does not work as the object x is not known.
Right.

> Still I
> would like to be able to pass a function as an argument that is
> evaluated using lazy loading.
If you rephrase your question more exactly and give a more elaborated 
example where you want to make use of it, we may be able to help, but I 
do not want to answer based on speculations here.

Best,
Uwe Ligges


> Can someone help?
>
> Thanks,
> Mark
> ???????????????????????????????????????
> Mark Heckmann
> Dipl. Wirt.-Ing. cand. Psych.
> Vorstra?e 93 B01
> 28359 Bremen
> Blog: www.markheckmann.de
> R-Blog: http://ryouready.wordpress.com
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

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Try this:
> foo2 <- function(x=2*y, y=x/2) eval(substitute(cat(x,y,"\n")))
> foo2(x = 1, y = x/3)
1 0.3333333
> foo2(x = y/2, y = 10)
5 10

On Wed, Mar 10, 2010 at 7:26 AM, Mark Heckmann <mark.heckmann at gmx.de>
wrote:
> I have the following function that makes use of lazy loading.
>
> foo <- function(x=2*y, y=x/2) cat(x,y)
>
> Now I want to be able to modify it like below:
>
> foo(y=x/3)
>
> Of course, this does not work as the object x is not known. Still I would
> like to be able to pass a function as an argument that is evaluated using
> lazy loading.
>
> Can someone help?
>
> Thanks,
> Mark
> ???????????????????????????????????????
> Mark Heckmann
> Dipl. Wirt.-Ing. cand. Psych.
> Vorstra?e 93 B01
> 28359 Bremen
> Blog: www.markheckmann.de
> R-Blog: http://ryouready.wordpress.com
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>