From luke at stat.uiowa.edu  Wed Oct 18 17:55:33 2006
From: luke at stat.uiowa.edu (Luke Tierney)
Date: Wed, 18 Oct 2006 10:55:33 -0500 (CDT)
Subject: [Rd] Error condition in evaluating a promise
In-Reply-To: <45364B0D.5060300@wald.ucdavis.edu>
References: <0359A469-1F7D-4CEF-A408-CCB185D5F90E@r-project.org>
	<6phvemixy1u.fsf@gopher4.fhcrc.org> <6phvemiuw3r.fsf@gopher4.fhcrc.org>
	<9AE19AAE-9CAD-4697-82DC-07724445114C@r-project.org>
	<45364B0D.5060300@wald.ucdavis.edu>
Message-ID: <Pine.LNX.4.64.0610181053420.21388@nokomis.stat.uiowa.edu>

Active bindings are another option (?makeActiveBinding).

It might be worth revisiting how promises are evaluated to see if at
elast a more sensible error message can be achieved, but making sure
any changes do not affect performance will be tricky.

Best,

luke

On Wed, 18 Oct 2006, Duncan Temple Lang wrote:

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> Hi Simon.
>
> One approach is RObjectTables. This provides a way to
> customize how variables are accessed/assigned in
> an environment and so allows an operation to do something
> to compute the value of a variable while still allowing
> it to be used as a variable rather than an explicit function
> call by the user.
>
> Otherwise, Seth's suggestion of an accessor function is the natural way.
> This does arise often and we need an extensible SEXP facility
> that allows us to capture some of the idioms that continue to arise.
>
> D.
>
> Simon Urbanek wrote:
>> Martin,
>>
>> On Oct 17, 2006, at 11:43 PM, Martin Morgan wrote:
>>
>>
>>> I believe the technique is to create an environment in the
>>> namespace, and then to access that through functions:
>>>
>>
>>
>> thanks, but this is not what I want (the symbols in the environment
>> are invisible outside) and it has nothing to do with the question I
>> posed: as I was saying in the previous e-mail the point is to have
>> exported variables in a namespace, but their value is known only
>> after the namespace was attached (to be precise I'm talking about
>> rJava here and many variables are valid only after the VM was
>> initialized - using them before is an error). I have an ugly work-
>> around for that as well, the question was whether promises could be
>> used for that purpose as a more clean solution and the answer appears
>> to be no - at least for R <=2.4.0.
>>
>> Thanks,
>> Simon
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>
> - --
> Duncan Temple Lang                    duncan at wald.ucdavis.edu
> Department of Statistics              work:  (530) 752-4782
> 4210 Mathematical Sciences Building   fax:   (530) 752-7099
> One Shields Ave.
> University of California at Davis
> Davis,
> CA 95616,
> USA
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> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

-- 
Luke Tierney
Chair, Statistics and Actuarial Science
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:      luke at stat.uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu




[Rd] Error condition in evaluating a promise
Luke Tierney