/usr/lib/mlton/sml/cml/TODO is in mlton-basis 20130715-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 | * Implement Okasaki real-time data-structures.
  + mailbox.sml -- needs functional queue
  + scheduler.sml -- needs imperative queue
  + timeout.sml -- needs functional priority queue
 |