primRnfNoErr can't ignore errors passed to primitives

[jmaessen]

I was fiddling with this as primRnfNoErr is a form of cheap-and-cheerful speculation (error-avoiding but not bottom-avoiding eagerness). But it was fairly obvious from reading eval.c that this was going to break:

module Example(main) where
import Prelude
import Primitives

main :: IO ()
main = do
  putStrLn "primRnfNoErr is kind of broken"
  return $! primRnfNoErr ((error "foo") + (3 :: Int))
  putStrLn "Success!"

And indeed:

% bin/mhs -r Example
primRnfNoErr is kind of broken
ERR: evalint, bad tag 2

Brainstorming a bit about how this might be solved cleanly. It'd be nice to be able to fix this without having to add checks at all the calls to evali etc.

[augustss]

Yeah, I know it's kinda broken. It's only(?) used for cprint, so it's not too bad.

If you can figure out a cheap way to unbreak it, that would be great.