MLton.Socket improvement

[Stephen Weeks]

> I don't understand your claim, but I think you were confused.  At the moment,
> the socket you do accept's on has to be closed by knowing that it is really
> a file descriptor and using Posix.IO.close on it.  If it were wrapped up in
> closures that you could never close that file descriptor.  I agree that the
> one you get as a result of an accept is wrapped into one of the streams so it
> will get get closed.  Did I miss something?

Ah.  I believe this is a bug in the current way sockets are done in
MLton.  Right now, the socket that is created by MLton.Socket.listen
is never closed.  You should fix that while you're at it.

> In the mean time, I seem to have gotten a way to convert a file descriptor
> into a TextIO.outstream in SML/NJ.  The only trick was that you have to provide
> both writeVec and writeArr functions, and for the latter there isn't a way
> to convert the CharArray into a Word8Array without doing a copy.

Please contribute this code to lib/mlton-stubs-in-smlnj/mlton.sml, the
MLton.TextIO.newOut function.