Re: [Rd] Capturing environment associated with a promise

From: Hadley Wickham <>
Date: Tue, 09 Oct 2012 10:58:35 -0500

> Both of these are possible in C. See:

Cool, thanks.

> It shows how to query an object to see if its a promise and but rather
> than extract the environment it shows how to copy a promise without
> evaluating it; however, it was also my experience that these two were
> what was actually needed rather than being able to extract the
> environment.
> I would also recommend you do some testing since I found that adding
> promises did not always make as big a difference in performance as I
> had hoped and the added complexity may not be worth it in all cases.
> For example, I had a version of proto that supported promises but
> ggplot2 only ran slightly faster with it so I did not pursue it any
> further. On the other hand if you are doing it to support
> self-referential structures then that is a different matter.

I'm mainly interested in this for pedagogy - giving students some tools to inspect promises without evaluating them would be useful.


RStudio / Rice University

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