[MLton] overloading

[Matthew Fluet]

> > Then we just (stable) sort the overloads by priority and resolve.
>
> I don't see why you need a stable sort but otherwise this makes
> sense.

Well, a stable sort preserves the order in which the overloaded
identifiers appeared in the source program.  I don't see why the overloads
need to be resolved in this order, but the resolve function in
overloads.sml:2224 specifically reverses the overloads list before
resolving each one.

> There is another approach, which is to implement a more powerful
> overloading resolution algorithm that considers all of the overloading
> to be resolved as a set of constraints and finds a solution (if there
> is one) to all the constraints at once.  Although more difficult than
> priorities, I might prefer that, since it has a less operational feel.
> But, since the overloading in SML is fixed and the priorities are
> sufficient to implement it, it feels a bit like a waste of time ...

I agree that overloading in SML is a bit broken and something more
powerful would be required if the overloading weren't fixed.