[MLton] Unicode... again

[Matthew Fluet]

> - For the time being I choose to ignore the basis' claim that "in 
> WideChar, the functions toLower, toLower, isAlpha,..., isUpper and, in 
> general, the definition of a ``letter'' are locale-dependent" and raise 
> an Unimplemented exception for these methods. I think the standard is 
> dreadfully misguided in assuming a global locale, and I defer what to do 
> here till later as it is what blocked my progress last time. (IMO these 
> functions have only questionable use, anyway)

Not to dismiss any of the thought and work already done, but I'm curious
why another 'obvious' interpretation of WideChar hasn't been explored. 
That is, why don't we take WideChar as an (admittedly brain-dead) 
wrapping of functions defined in <wchar.h>.  These descriptions of these 
functions seem to match the Basis Library descriptions, in that they 
have a notion of the current locale.  Admittedly, WideChar wouldn't 
provide access to changing the locale (the setlocale function), but this 
would seem consistent with other portions of the SML Basis Library that 
provides just a thin veneer over corresponding POSIX functions.