[R] best practice(s) for retrieving a local variable from a closure

[Gabor Grothendieck]

On Fri, Apr 8, 2011 at 9:48 PM, Benjamin Tyner <btyner at gmail.com> wrote:
> Greetings,
>
> Say I have defined
>
>  mp <- function(a) function(x) x^a
>
>  f2 <- mp(2)
>
> and I would like to retrieve the "a" which is local to f2. Two options come
> to mind;
>
>  get("a", envir=environment(f2))
>  eval(substitute(a), environment(f2))
>
> I'm curious if one of these is preferred over the other in terms of
> efficiency, robustness, aesthetics, etc. Or perhaps someone can share
> another way to skin this cat, besides wrappers around eval() like
>
>  evalq(a, environment(f2))
>  with(environment(f2), a)
>
> Also, I'd like to confirm that I have used the correct terminology in the
> subject line, that "a" is a local variable with respect to f2, which is a
> closure?
>

Solutions involving eval tend to be less preferred.  "a" is termed a
free variable of f2.

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