Re: GNU Guile 2.9.9 Released [beta]

[Mikael Djurfeldt <mikael@djurfeldt.com>]

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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 <wingo@pobox.com> skrev:

> On Tue 14 Jan 2020 13:18, Mikael Djurfeldt <mikael@djurfeldt.com> 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
>

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