[MLton] CML

[Stephen Weeks]

> (Although, I think this is a design problem that can be easily fixed.  The
> transaction id datatype is always paired with some data (usually a CML
> thread and maybe some associated data) that predicates as being either
> still a valid transaction or a cancelled transaction.  If we made the
> trans_id datatype an essentially an 'a option ref, then the paired data
> could be held within the trans_id and would automatically become
> unreachable when the transaction is cancelled.)

To make sure I understand, since the same trans_id can be paired with
lots of different data, this approach requires keeping a list of all
pairs associated with the trans_id so that when it is cancelled, you
can walk the list and clear all the option refs.  Heck, at that point,
why not remove the cancelled pair from the queue it is in?  This would
require more mutable queues, but that's not too hard.