real-life identity and "=="

Michael Hudson mwh21 at
Sun May 14 15:32:43 EDT 2000

weeks at ((Greg Weeks)) writes:

> Now, I agree that comparing the *contents* of lists is sometimes useful.
> But "==" should not be the way to do it (just as "=" is not the way to copy
> contents).
> In practice, it doesn't much matter.  But it itches.  So close!
> Greg
> PS: Java has a similar problem.  For BitSets for example, the equals() and
> hashCode() methods erroneously assume immutability.  Again, so close.

Common Lisp has eq, eql, equal and equalp which are all different ways
of testing equality - and that's probably not enough for a completely
general solution.  There is a reason for this; equality is not as
clearly a defined operation as one might think.

BTW, eql is almost exactly what you are asking for in Python.

unhelpful-ly y'rs

40. There are two ways to write error-free programs; only the third
one works.
     -- Alan Perlis,

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