From @|mon@urb@nek @end|ng |rom R-project@org  Mon Mar  8 03:51:00 2021
From: @|mon@urb@nek @end|ng |rom R-project@org (Simon Urbanek)
Date: Mon, 8 Mar 2021 15:51:00 +1300
Subject: [Rd] An argument promise containing bytecode?
In-Reply-To: <7DD4C301-1849-4BAF-9C46-3256F09F79C9@uzh.ch>
References: <7DD4C301-1849-4BAF-9C46-3256F09F79C9@uzh.ch>
Message-ID: <E410AC79-00DF-456B-91F4-9AC0FFB135A6@R-project.org>

Taras,

I don't think this has anything to do with promises, rather it is called Just-In-Time (JIT) compilation - see ?enablleJIT in R, it is enabled by default, so the function will be compiled on second use.

Cheers,
Simon



> On Mar 7, 2021, at 11:12 PM, Taras Zakharko <taras.zakharko at uzh.ch> wrote:
> 
> Dear all, 
> 
> I was playing around with some C code that inspects argument promises and I noticed that forwarded arguments sometimes contain bytecode in the PRCODE component. E.g. if I have a nested call like this:
> 
>  f <- function(x) x
>  g <- function(x) f(x)
> 
> g(1+1)
> 
> and inspect the value of ?x? in g?s frame from within f?s frame (basically calling findVar(parent.frame(), x)), I would see a LANGSXP the first time g()  is invoked, but BCODESXP on every subsequent time.  Using PREXPR gets me the original LANGSXP in any case. 
> 
> Now, this is curious behavior and I had a quick glance into R source code related to closure evaluation and argument matching, but I could not see anything that would generate bytecode for promises. Could someone with in-depth knowledge of R?s machinery explain what is going on? 
> 
> Thanks, 
> 
> Taras
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[Rd] An argument promise containing bytecode?
Simon Urbanek