From vitekj at icloud.com  Thu Jan  4 09:20:49 2018
From: vitekj at icloud.com (jan Vitek)
Date: Thu, 04 Jan 2018 03:20:49 -0500
Subject: [Rd] Coping with non-standard evaluation in R program analysis
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Message-ID: <D3275CAA-9051-499D-92A8-69408D3D7263@icloud.com>

Hi Evan,

You may find some parts of what we are doing with genthat useful.  Genthat is a tool
for creating unit tests by recording argument and return values of calls. This is
done by instrumentation of the source code.

The git repo with the code is here https://github.com/PRL-PRG/genthat

We don?t really deal with NSE though. It could be something worth thinking about for us.
The contact for genthtat is Filip.


We are also writing a tool for analyzing promises and generating execution traces
within the R VM.  This is available in 
    https://github.com/PRL-PRG/R-dyntrace

Aviral and Konrad are the contacts there.


Best,

jan






Jan Vitek, Professor 
Computer Science, 
Northeastern University

> On Jan 3, 2018, at 7:18 PM, Peter Meilstrup <peter.meilstrup at gmail.com> wrote:
> 
> 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
> <epatters at 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]]
>> 
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
> 
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[Rd] Coping with non-standard evaluation in R program analysis
jan Vitek