[MLton] WideChar?

[Matthew Fluet]

> As  you say, the fact that a unicode code needs more than 4 nibbles is really
> a problem.  You cannot make the number  of  hex  characters  in  \u  variable
> because then it is ambiguous (because you can't tell where the character code
> ends).  Always requiring 8 hex digits would really be even more onerous  than
> just the fact that you need to use \u at all.

Again, for expedience, one might (gasp) extend the lexical defintion to
allow \Uxxxxxxxx, which would let you write down any Unicode string.
If you happen to fall in the low (plane / codepage / whatever terminology
is correct), then you can use \uxxxx.