[bachmeier]

> Most the tasks that require heavy computation in R are done through C/C++/Fortran APIs - why can't D interface with them without the intermediate R layer?

You absolutely can do that, but it's generally not a fun experience. Most of the time the overhead of calling into R is trivial. In that case, take advantage of the convenience of R and get on to other things. There's also a lot of pure R code that you don't have any other way to call.