For 2), it is not exposed in R's standard library but it is exposed in
the Rinternals API. A promise that is forced in normal evaluation will
have PRENV set to NULL.
Peter
On Tue, Jan 2, 2018 at 4:19 PM, Evan James Patterson
<epatt...@stanford.edu> wrote:
> Hello R experts,
>
>
> I plan to develop a tool for dynamic analysis of R programs. I would like to
> trace function calls at runtime, capturing argument and return values.
> Following a suggestion made some time ago on this list, my high-level
> implementation strategy is to rewrite the AST, augmenting call expressions
> with pre-call and post-call shims to capture the arguments and return value,
> respectively.
>
>
> I can think of only one fundamental conceptual obstacle to this approach: R
> functions are not necessarily referentially transparent. The arguments
> received by a function are not values but promises. They can be evaluated
> directly ("standard evaluation"), after applying arbitrary syntactic
> transformations ("non-standard evaluation", aka NSE), or not at all.
> Therefore, if you peek at the values of function arguments before evaluating
> the function, you risk altering the semantics of the program, possibly
> fatally.
>
>
> I'm looking for general advice about how to cope with NSE in this context. I
> also have some specific questions:
>
>
> 1) Is it possible to determine whether a given function (primitive, in R, or
> external) uses NSE on some or all of its arguments?
>
>
> 2) Is it possible to inspect the promise objects received by functions, say
> to determine whether they have been evaluated, without actually evaluating
> them? The R manual is not encouraging in this area:
>
>
> https://cran.r-project.org/doc/manuals/r-release/R-lang.html#Promise-objects
>
>
> Thank you,
>
>
> Evan
>
>
> [[alternative HTML version deleted]]
>
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