[MLton] flattening of arrays and vectors

[Henry Cejtin]

With  regards  to distributing the basis library sources and ways to make the
saved world after changing it, I agree that that is very important.

As to file identity, I would think that the way to go is to use  a  timestamp
and  re-scan  the file if it is newer.  My notion is that you scan the source
names, recording their current identity (device/inode) and  also  looking  at
the  timestamp.   If  they  are newer than the saved world memory of the time
then you issue a warning and scan the sources.

Mind you, I have no idea how hard that would be to do in the  current  world,
but at least conceptually it seems pretty straight forward.