Re: [Rcpp-devel] calling and R function from rcpp and evaluation
Hi Antonio,
This is about how R evaluation works. Might not just be what you think it is.
When you use Rcpp and therefore .Call things are evaluated fairly early, at
least earlier than what would happen with R, etc … you can reproduce what R
does by using promises. For example this work in Rcpp11:
// [[Rcpp::export]]
RawVector rcpp_serialize(Dots dots){
Function serialize(serialize) ;
return serialize( dots.promise(0), R_NilValue ) ;
}
Dots has not been implemented in Rcpp, but would not be too hard to port:
https://github.com/romainfrancois/Rcpp11/blob/master/inst/include/Rcpp/Dots.h
But it would also need to fix Rcpp’s handling of recursive promises (i.e.
promise of a promise of a promise).
Alternatively, for a solution based on Rcpp, you can look in dplyr. The
.data_dots function has most of the R-level logic
https://github.com/hadley/dplyr/blob/master/R/manip-df.r
And the C++ logic is mostly in DataDots.h
https://github.com/hadley/dplyr/blob/master/inst/include/tools/DataDots.h
Romain
Le 6 févr. 2014 à 02:07, Antonio Piccolboni anto...@piccolboni.info a écrit :
Hi,
I was wondering why I can serialize a call such as in
serialize(call(ripley), NULL)
[1] 58 0a 00 00 00 02 00 03 00 02 00 02 03 00 00 00 00 06 00 00 00 01 00 04
00 09 00 00 00 06 72 69 70 6c 65 79 00 00 00 fe
but if I try from C++ the call gets evaluated
library(Rcpp)
rcpp.serialize = cppFunction(code=RObject my_serialize(RObject x){Function
r_serialize(\serialize\); return r_serialize(x, R_NilValue);})
rcpp.serialize(10)
[1] 58 0a 00 00 00 02 00 03 00 02 00 02 03 00 00 00 00 0e 00 00 00 01 40 24
00 00 00 00 00 00
# easy things work
rcpp.serialize(call(ripley))
Error: could not find function ripley
# wants to evaluate it
unserialize(rcpp.serialize(call(sqrt, 2)))
[1] 1.414214
# How is one to serialize the call itself
rcpp.serialize(list(call(ripley)))
[1] 58 0a 00 00 00 02 00 03 00 02 00 02 03 00 00 00 00 13 00 00 00 01 00 00
00 06 00 00 00 01 00 04 00 09 00 00 00 06 72 69 70 6c 65 79 00 00 00 fe
#wrapping in a list is enough to stop evaluation
eval(call(ripley))
Error in eval(expr, envir, enclos) : could not find function ripley
eval(list(call(ripley)))
[[1]]
ripley()
#OK that's consistent
Could anyone enlighten me on the evaluation mechanism? Not saying it's
broken, but certainly my expectations were off. Thanks
Antonio
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[Rcpp-devel] calling and R function from rcpp and evaluation
Hi,
I was wondering why I can serialize a call such as in
serialize(call(ripley), NULL)
[1] 58 0a 00 00 00 02 00 03 00 02 00 02 03 00 00 00 00 06 00 00 00 01 00 04
00 09 00 00 00 06 72 69 70 6c 65 79 00 00 00 fe
but if I try from C++ the call gets evaluated
library(Rcpp)
rcpp.serialize = cppFunction(code=RObject my_serialize(RObject
x){Function r_serialize(\serialize\); return r_serialize(x,
R_NilValue);})
rcpp.serialize(10)
[1] 58 0a 00 00 00 02 00 03 00 02 00 02 03 00 00 00 00 0e 00 00 00 01 40
24 00 00 00 00 00 00
# easy things work
rcpp.serialize(call(ripley))
Error: could not find function ripley
# wants to evaluate it
unserialize(rcpp.serialize(call(sqrt, 2)))
[1] 1.414214
# How is one to serialize the call itself
rcpp.serialize(list(call(ripley)))
[1] 58 0a 00 00 00 02 00 03 00 02 00 02 03 00 00 00 00 13 00 00 00 01 00
00 00 06 00 00 00 01 00 04 00 09 00 00 00 06 72 69 70 6c 65 79 00 00 00 fe
#wrapping in a list is enough to stop evaluation
eval(call(ripley))
Error in eval(expr, envir, enclos) : could not find function ripley
eval(list(call(ripley)))
[[1]]
ripley()
#OK that's consistent
Could anyone enlighten me on the evaluation mechanism? Not saying it's
broken, but certainly my expectations were off. Thanks
Antonio
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Re: [Rcpp-devel] calling and R function from rcpp and evaluation
On 5 February 2014 at 17:07, Antonio Piccolboni wrote:
| Hi,
| I was wondering why I can serialize a call such as in
|
| serialize(call(ripley), NULL)
| [1] 58 0a 00 00 00 02 00 03 00 02 00 02 03 00 00 00 00 06 00 00 00 01 00 04 00
| 09 00 00 00 06 72 69 70 6c 65 79 00 00 00 fe
|
| but if I try from C++ the call gets evaluated
|
| library(Rcpp)
|
| rcpp.serialize = cppFunction(code=RObject my_serialize(RObject x){Function
| r_serialize(\serialize\); return r_serialize(x, R_NilValue);})
|
| rcpp.serialize(10)
| [1] 58 0a 00 00 00 02 00 03 00 02 00 02 03 00 00 00 00 0e 00 00 00 01 40 24
| 00 00 00 00 00 00
| # easy things work
|
| rcpp.serialize(call(ripley))
| Error: could not find function ripley
| # wants to evaluate it
|
| unserialize(rcpp.serialize(call(sqrt, 2)))
| [1] 1.414214
| # How is one to serialize the call itself
|
| rcpp.serialize(list(call(ripley)))
| [1] 58 0a 00 00 00 02 00 03 00 02 00 02 03 00 00 00 00 13 00 00 00 01 00 00
| 00 06 00 00 00 01 00 04 00 09 00 00 00 06 72 69 70 6c 65 79 00 00 00 fe
| #wrapping in a list is enough to stop evaluation
|
| eval(call(ripley))
| Error in eval(expr, envir, enclos) : could not find function ripley
| eval(list(call(ripley)))
| [[1]]
| ripley()
|
| #OK that's consistent
|
|
| Could anyone enlighten me on the evaluation mechanism? Not saying it's broken,
| but certainly my expectations were off. Thanks
Did you look at eg Section 4: Function Calls in the Rcpp-introduction
vignette?
Besides Rcpp::Function you could also try the Rcpp::Language class, which is
shown there. We now also have an Rcpp::Promise class, but I have not yet used
it.
And in all those years with Rcpp I don't think I have used, or thought I
needed, delayed evaluation at the C++ level. But I suspect that for example the
recent dplyr package does something along those lines, so you could look there.
Dirk
--
Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com
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