Re: Are fixnums guaranteed to be `eq?` whenever they are `=`/`equal?` ?

At Mon, 14 Mar 2016 19:43:51 -0400, Tony Garnock-Jones wrote:
> Can I rely on the truth of the following:
> 
>   (implies (and (fixnum? x) (fixnum? y) (= x y))
>            (eq? x y))
> 
> ?

Yes, that's guaranteed by the docs.


> I know I can rely on something similar for symbols.

And keywords.


> What other sorts of values can I rely on eq? being an appropriate
> equivalence predicate for?

Booleans, void, and characters with a scalar value under 256.

Opaque objects like custodians and inspectors are also `equal?` only
when they are `eq?`, but I'm not sure if that's the kind of thing
you're looking for.

Literal numbers, characters, strings, byte strings, or regular
expressions in a program are also `eq?` when they are `equal?`, since
they're interned. That's an property of where the values came from,
though, as opposed to a property of the kind of value.

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