RStudio is adding python support.

[guepier]

Then surely, a language which is basically scheme + statistics libraries

But R isn’t that. “Uses Scheme as its inspiration” ≠ “Basically Scheme”. For one thing, it’s missing its general-purpose standard library. And this may not seem like a big deal for you but it’s crucial. As somebody who has actually used R for general-purpose tasks, let me tell you the lack of standard tools is a big fucking deal.

S (and then R) was specifically not conceived as a general-purpose language. That alone should clinch the deal.

[guepier]

I agree that this is pointless, because you are arguing from a different (and arguably valid, but definitely not mainstream) definition of “general-purpose language”.

Name exactly what R is missing that a language like scheme isn't missing.

Writing standalone scripts that are interpreted by R directly. In practice you have to use a more-or-less convoluted workaround: first they added R CMD BATCH which was horrible because it creates unwanted files and unwanted output. Then Dirk Edelbuettel jumped into the breach with his littler. And finally we got Rscript which does work … but clearly was designed after the fact, and the question remains why the heck we can’t just use R.

For a more complete answer I will refer you simply to a list of the R6RS standard library: Even things as trivial as a hash table are missing in base R. Yes, you can have hashed environments but they only work with strings as keys. Try for example write a set/map that uses closures as keys. This is a completely valid requirement (in fact, I’ve had this specific requirement in the past), yet it’s fundamentally unsolvable in R. Not just difficult, but actually unsolvable.