The opaque: flag causes a change in the behavior of equal? and equal?-hash . When the opaque: flag is not used, two structures are equal? if they have the same type and each field is equal? in both structures. When the opaque: flag is used, two structures are equal? only if they are eq? (i.e. the same instance).

Awesome and very useful!

So the code that checks for the opaque: flag in the Gambit sources is found in the equal? and equal-hash? definitions...

Thank you, Marc