TRADE — Hole in trader constraint language

We have a hole in the trader constraint language:

interface I1 {
enum

;
};

interface I2 {
enum

;
};

The expression

$.field_name == red

is ambiguous because it's not clear which red is meant. You could argue
that the type of the field on the left will identify what type should
apply for the enumerator on the right. However, that doesn't solve the
problem because

red == red

is a valid expression.

Attempts to solve the problem by using a scoped name don't work:

$.field_name == I1::red

That's because the grammar does not allow the use of the :: operator.