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Alexey Radul scripsit: > I don't think that's right. The whole point of boxes is to be > mutable; which means the correct treatment  thereof by equality > predicates is to compare by identity. Henry Baker's `egal?`, though I like it very much, is not "the correct treatment", in the sense of the only possible or reasonable treatment, of equality. There is a place for it, yes; but there is also a place for contingent equality. "Is the value in that box (of money, say) equal to the value in this box?" is not an ill-posed question, and it is this kind of equality that `equal?` provides in Scheme as it is. By your argument, since vectors are also usually used for their mutability, `equal?` should reduce to `eqv?` on them too, yet this has never been so. In short, `equal?` is and always will be flawed. A generalized equality predicate that can be tailored to specific applications is needed. I think I'll push that ahead of hash tables, which I was planning to do next. >  http://www.pipeline.com/~hbaker1/ObjectIdentity.html -- An observable characteristic is not necessarily John Cowan a functional requirement. --John Hudson cowan@xxxxxxxx