D-Link with R/MATLAB/Julia/SQL

[bachmeier]

On Saturday, 7 December 2013 at 17:08:49 UTC, Joseph Rushton 
Wakeling wrote:
> On 06/12/13 03:16, bachmeier wrote:
>> I have been using R and D together for several months. It is 
>> easy to embed
>> either inside the other. Unfortunately I have not found the 
>> time to write up any
>> decent notes about it. With the latest release of DMD, my 
>> workflow is to create
>> shared libraries with D and call them from R. Using the .C 
>> interface from R is
>> simple, but not much fun. I wrote up a few notes here:
>>
>> http://lancebachmeier.com/wiki/doku.php?id=rlang:calling-d
>
> That's very cool, and also something of a relief to see, as I 
> think interfacing nicely with R is an essential feature for a 
> programming language in some domains of research.
>
>> What I've been working on lately is a .Call-based interface 
>> that provides some
>> of the same convenience as Rcpp. I call into Gretl's C API to 
>> get a wide range
>> of econometric functions. It works well enough that I'm going 
>> to give a lecture
>> to my graduate students on calling D functions from R next 
>> week.
>>
>> To embed R inside D, which is maybe more what you're after, I 
>> created a simple C
>> interface to RInside. That works well. Unfortunately I don't 
>> have notes on that
>> either.
>>
>> I'll be happy to share more if any of this will help you.
>
> I think that you would be doing everyone a big favour if you 
> would provide a good writeup on this.  Can I also suggest 
> making a talk proposal to DConf 2014 about this work?

I will write something up as soon as I can, but it might be a 
while before that happens. I will also share my code for the 
.Call interface. Hopefully I will get feedback from someone more 
knowledgeable about D.

I'll leave DConf to the experts. I'm an economist who taught 
himself to program.

> Question: I remember a colleague who had worked on linking a C 
> library into R telling me that he'd had to make copies of data 
> before passing into R, because R expects variables to be 
> immutable.  Is there anything that you can do with D's support 
> for immutability that lets you avoid this?  Or are you 
> constrained by the fact that you need to use an extern(C) API?

Your colleague might well be right, but I'm not familiar with 
that issue. In the other direction (R to C) you want to copy the 
data before mutating. Suppose you have

x <- c(1,2,3)
y <- x
.Call("foo", y)

R does a lazy copy of x into y, such that y is a pointer to x 
until the copy is actually needed. In this example, when you pass 
y from R to C, all you're passing is a pointer to the struct 
(SEXP). On the C side, you can do anything you want with that 
pointer, and it will modify both y and x unless you make a copy 
of y.

You can create an SEXP on the C side and pass it into R, but 
that's a bit clumsy so I avoid it. Whether I'm embedding R in 
C/C++/D or vice versa I do the allocation in R. Moving data 
between R and D is nothing more than passing a pointer around.