On 01/09/2010 02:04 AM, Guillaume Yziquel wrote:
Guillaume Yziquel a écrit :
Simon Urbanek a écrit :
If you have suggestions for extending the API, feel free to post them
with exact explanations how in general that extensions could be
useful (general is the key word here - I think so far it was rather
to hack around your way of implementing it). [And FWIW tryEval *is*
part of the API].
Concerning tryEval, I had a look at context.c, and it says:
/*
R_tryEval is in Rinternals.h (so public), but not in the API.
*/
And concerning tryEval, there's one feature I miss: there is error
handling capabilities, but to my knowledge, it provides a boolean status
back. True or false. Is it possible to get a full error message back, so
that it can be analysed and translated to OCaml exceptions?
Not to my knowledge, what we do in Rcpp is to to bring the expression to
the R side, evaluate it within a tryCatch and then grab either the
result if successfull, or the error.
The R side of this is in :
http://r-forge.r-project.org/plugins/scmsvn/viewcvs.php/pkg/R/exceptions.R?rev=249&root=rcpp&view=markup
and the C++ class is the Evaluator class:
http://r-forge.r-project.org/plugins/scmsvn/viewcvs.php/pkg/src/Evaluator.cpp?rev=260&root=rcpp&view=markup
It smells the "it works but ..." pattern.
tryEval is just a thin wrapper around R_ToplevelExec (in context.c),
what you need (and we need also in Rcpp) is a somewhat improved version
of R_ToplevelExec which would modify the context. This would remove the
need for a round trip to the R side...
I once tried to factor R_ToplevelExec out of R into a package, but
failed. When I get a better understanding of contexts, I might propose
something.
Now, here's a feature I'd like to implement with the API:
In OCaml, there's a library called Lwt. It's a library implementing
lightweight, or green, threads.
What I want to do is to be able to launch some R code, and have it
multithread with other OCaml code, within one single real thread.
Therefore I have to implement the commutation context somewhere in the
evaluation mechanism of R itself.
The API doesn't support that, I guess.
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
|- http://tr.im/JOlc : External pointers with Rcpp
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`- http://tr.im/IW9B : C++ exceptions at the R level
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