> The only solution i see it may be to add into VM a stack check for
> detecting repetitive patterns.

That doesn't make sense.

As a programmer one should know what recursion is. One should also
know what it means to have circular references. Comparing two objects
using #= doesn't make much sense, unless you know exactly what the #=
is doing. Unfortunately every class in Squeak implements it with a
different philosophy and even worse (a = b) = (b = a) is sometimes
even false.

The Squeak collections try to be super smart with the #=, but
obviously they are not smart enough for the given examples.
VisualWorks doesn't implement #= in Collection and therefore uses #==.
In my opinion this makes a lot of sense. Collections are such a
generic container that they cannot be compared as is for all possible
uses. I found myself implementing special comparison operators many
times already.

This is exactly the same as for copying (as discussed a few months
ago). Sometimes you want ...

- an equality comparison #==
- a shallow comparison
- a deep comparison
- a very deep comparison (following the terms in the copy protocol)
- sometimes you want to ignore certain values
- sometimes you want to stop a certain places or after a certain time
- etc.

There is simply not a single solution that works for all.

Cheers,
Lukas

-- 
Lukas Renggli
http://www.lukas-renggli.ch