> I can also see the argument that for an _extension_, a syntax that
> isn't easily mistaken for ML is a win.
We've already got "_" before the keyword to do that. I think the
analogy with the usual use of ":" is pretty strong. In fact, that's
what we started with originally with _ffi (which became _import).
It's just that we got clever to save a few keystrokes ("-> unit") when
we added _export.