[MLton] Int.fmt thread unsafe? (YUCK)

[Stephen Weeks]

> But note the implications of this: you cannot use Int.fromString in
> a signal handler.

Actually it's Int.toString.  But I agree with your point.  And it is a
bad situation.  However, one can easily wrap Int.toString in a
critical section (e.g. use MLton.Thread.atomically) and produce a safe
version.  I can't think of anything better in our current state.

It would certainly be helpful if we were to provide a thread-safe
basis library wrapper with the MLton package.  I don't know if anyone
has gone to the trouble to start to build one yet.