In article <E9GJ9z.Ety@ecf.toronto.edu>, email@example.com (Patrick
> >> Can you give an example of two immutable objects, alike in every way,
> >>which need to be distinguished?
> Neither does the GC. It can simply throw away one of the objects
> immediately and use the other, can't it?
Indeed. One could do this trivially by means of a 'hash-consing' copying
GC. The idea is that when you 'copy' the node, you hash-cons it in the
new space. Since hash-consing uniquizes the object recursively, any 'like'
objects will find themselves EQ after the GC.
Your mileage will vary on circular immutable objects.