[polyml] Poly/ML and SML/NJ warn inconsistently about using op for an infix constructor

For example, given

infix & datatype t = &

Poly/ML (5.4) reports:

Warning-(&) has infix status but was not preceded by op.

So Poly/ML seems to prefer the use of 'op' in a datatype declaration. However, if 'op' is present, i.e.

datatype t = op &

SML/NJ (110.73) reports:

stdIn:2.14-2.16 Warning: unnecessary `op'

Generally, it is a good principle to avoid warnings but, in this particular respect, that isn't possible for code that is shared between Poly/ML and SML/NJ. Note that MLton (20100608) doesn't warn either way.

Does the Standard provide any guidance about the use of op here? Can anything be done to align the warnings from Poly/ML and SML/NJ in this respect?

Thanks, Phil