Re: GNU Guile 2.9.9 Released [beta]

[Mikael Djurfeldt]

Hmm... it seems like both Stefan and you have interpreted my post exactly the opposite way compared to how it was meant. :)

I completely agree that procedure equality is not strongly connected to the first citizen-ness.

What I wanted to say is that I probably prefer you to *reverse* the recent patch because I prefer to have good optimization also when procedures are referenced by value in more than one non-operator position. I prefer this over having (eq? p p) => #t for the reasons I stated.

Best regards,

Mikael

Den tis 14 jan. 2020 15:33Andy Wingo <address@hidden> skrev:

On Tue 14 Jan 2020 13:18, Mikael Djurfeldt <address@hidden> writes:

> I probably don't have a clue about what you are talking about (or at
> least hope so), but this---the "eq change"---sounds scary to me.
>
> One of the *strengths* of Scheme is that procedures are first class
> citizens. As wonderfully show-cased in e.g. SICP this can be used to
> obtain expressive and concise programs, where procedures can occur
> many times as values outside operator position.
>
> I would certainly *not* want to trade in an important optimization
> step in those cases to obtain intuitive procedure equality. The risk
> is then that you would tend to avoid passing around procedures as
> values.

Is this true?

  (eq? '() '())

What about this?

  (eq? '(a) '(a))

And yet, are datums not first-class values?  What does being first-class
have to do with it?

Does it matter whether it's eq? or eqv?

What about:

  (eq? (lambda () 10) (lambda () 10))

What's the difference?

What's the difference in the lambda calculus between "\x.f x" and "f"?

What if in a partial evaluator, you see a `(eq? x y)`, and you notice
that `x' is bound to a lambda _expression_?  Can you say anything about
the value of the _expression_?

Does comparing procedures for equality mean anything at all?
https://cs-syd.eu/posts/2016-01-17-function-equality-in-haskell

Anyway :)  All that is a bit of trolling on my part.  What I mean to say
is that instincts are tricky when it comes to object identity, equality,
equivalence, and especially all of those combined with procedures.  The
R6RS (what can be more Schemely than a Scheme standard?) makes this
clear.

All that said, with the recent patch, I believe that Guile 3.0's
behavior preserves your intuitions.  Bug reports very welcome!

Andy