What do you mean by 'low-level extensions'? There's nothing in the language proper that can't run on bare metal, how much lower can you get? If anything, it's

What do you mean by 'low-level extensions'? There's nothing in the language proper that can't run on bare metal, how much lower can you get? If anything, it's the functional parts that feel bolted on: closures are crippled (though getting better soonish), the types that get spit out of iterator chains are hideous, no currying, no HKTs, functional data structures are much harder to write w/o a gc, etc.