"Simon Marlow"
I think, having the third point is good, because the Haskell report requires that
Computation exitWith code terminates the program, returning code to the program's caller.
Either way we still conform to the report in the case of a single threaded program (actually, we've already deviated from the report in allowing you to catch the ExitException and carry on).
For a multi-threaded program, it's not clear to me what exitWith should do. What should happen if a Haskell callback invokes exitWith? Should it terminate the Haskell main thread?
I must admit I'm leaning more towards omitting the third point, and that's what I've implemented for now.
If you call exit() in a multi-threaded C program, it is also gone. Cheers, Manuel