[polyml] Type inference issue with phantom types

I have been making use of phantom types (for encoding a single-inheritance class hierarchy) and have encountered a case where code accepted by MLton does not type check with Poly/ML. After investigating, it appears that MLton, Poly/ML and SML/NJ all take different views on what is a valid program!

Attached are two small examples with a slight difference where type checking accepts/rejects as follows:

test-1.sml test-2.sml

MLton 20100608 accept accept Poly/ML 5.4, latest reject accept SML/NJ 110.73 reject reject

I don't know which of the above is consistent with the Definition yet. (I would be very glad if test-1 is a legal program though!)

Phil