equality

[veldhvz]

On my question
>A question: "Is it possible to implement in Clean
>an operator that checks for token-identity?"

Hamilton Richards Jr. wrote:
>The question calls for making an explicit distinction between two kinds of
>equality-- extensional equality (often called "equivalence") and
>intensional equality (often called "identity"). Obviously identity implies
> ...

Where I replied:
>Thank you for pointing this out to me. I was aware that something
>like this might be the case, but I didn't see exactly what was 
>the problem
> ...
> Why isn't there a restriction defined on the instances of the
> == operator so that x==x  must always yield True?
> This restriction would allow the compiler to make the suggested
> optimization.

Or rather, why isn't there a predefined equality operator
on all types, that merely checks whether the normal forms
of its arguments are structurally the same.
This operator could easily be implemented in a way that
exploits token-identity.

-- 
Gert Veldhuijzen van Zanten
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