Modules don’t have a built-in foreign function interface yet but it is possible to integrate C++ code via the excellent Rcpp package.

As an example, take a look at the rcpp module found under inst/doc; the module consists of a C++ source file which is loaded inside the __init__.r file:

Rcpp::sourceCpp(module_file('convolve.cpp'), env = environment())

Here’s the C++ code itself (the example is taken from the Rcpp documentation):

#include "Rcpp.h"

using Rcpp::NumericVector;

// [[Rcpp::export]]
NumericVector convolve(NumericVector a, NumericVector b) {
    int na = a.size(), nb = b.size();
    int nab = na + nb - 1;
    NumericVector xab(nab);
    for (int i = 0; i < na; i++)
        for (int j = 0; j < nb; j++)
            xab[i + j] += a[i] * b[j];
    return xab;
}

This module can be used like any normal module:

rcpp = import('rcpp')
ls(rcpp)

## [1] "convolve"

rcpp$convolve(1 : 3, 1 : 5)

## [1]  1  4 10 16 22 22 15

Unfortunately, this has a rather glaring flaw: the code is recompiled for each new R session. In order to avoid this, we need to compile the code once and save the resulting dynamic library. There’s no straightforward way of doing this, but Rcpp wraps R CMD SHLIB.

For the time being, we manually need to trigger compilation by executing the __install__.r file found in the inst/doc/rcpp module path.

Once that’s done, the actual module code is easy enough:

# Load compiled module meta information, and load R wrapper code, which, in
# turn, loads the compiled module via `dyn.load`.
load_dynamic = function (prefix) {
    context = readRDS(module_file(sprintf('%s.rds', prefix)))
    source(context$rSourceFilename, local = parent.frame())
}

load_dynamic('convolve')

We can use it like any other module:

compiled = import('rcpp/compiled')
compiled$convolve(1 : 3, 1 : 5)

## [1]  1  4 10 16 22 22 15