[MLton] Non-exhaustive exn fn match

[Vesa Karvonen]

Quoting "Wesley W. Terpstra" <wesley@terpstra.ca>:

> > > > It is much better to just avoid unnecessary shared state, IMHO.
> 
> If it is unnecessary, then I completely agree.

To clarify: In this case, there exists an obvious, simpler solution that
offers competitive performance (both time and space) and does not rely on
shared state (in inject & project), hence I consider the use of shared
state unnecessary.

-Vesa Karvonen