From spinuvit.list at gmail.com  Wed Aug 18 01:13:44 2010
From: spinuvit.list at gmail.com (Vitaly S.)
Date: Wed, 18 Aug 2010 01:13:44 +0200
Subject: [Rd] parent.frame(1) of a S4 method is not a calling
	environment.
References: <87d3tj4ku4.fsf@gmail.com> <4C698DAC.3090704@fhcrc.org>
	<87wrrq2ns2.fsf@gmail.com> <4C6A630C.9020802@gmail.com>
Message-ID: <87sk2c3k9j.fsf@gmail.com>

Duncan Murdoch <murdoch.duncan at gmail.com> writes:

> Vitaly S. wrote:
>> Martin Morgan <mtmorgan at fhcrc.org> writes:
>>   
>>>> So,  can I be sure that for such functions parent.frame(2) will always work?
>>>> What are the additional rules?
>>>>       
>>> callNextMethod() will cause additional problems; the idea that you'll
>>> grab things from somewhere other than function arguments doesn't seem
>>> like a robust design, even if it's used in some important parts of R.
>>>
>>> Martin
>>>
>>>     
>>
>> That make it difficult to handle unevaluated expressions in methods. A solution
>> would be to explicitly require the users to use quote() or expression(),  and
>> then to use the "expression" in the signature. Slightly unpleasant, though.
>>
>>   
>
> You could use formulas for that.  If you pass in
>
> formula = ~ x + y*z
>
> then environment(formula) will be the right evaluation environment, and formula[[2]] will be the unevaluated x +
> y*z.
>
> Duncan Murdoch

Thank you Duncan, I didn't know that.

For programmatic use though, formula interface is slightly inconvenient. A
specialized function and class would be desirable. With the advent of more and
more complex S4 classes, unevaluated expressions in methods calls will became a
necessity, that's my feeling.

Thank you.
Vitaly.

>
>> Standardised, simpler syntax like .() in  ggplot and plyr,  would be handy here.
>> Hopefully .() is not grabbed for something else in meanwhile:).
>>
>> Vitaly.
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>



[Rd] parent.frame(1) of a S4 method is not a calling environment.
Vitaly S.