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Fwd: GNU Guile 2.9.9 Released [beta]

From: Stefan Israelsson Tampe
Subject: Fwd: GNU Guile 2.9.9 Released [beta]
Date: Tue, 14 Jan 2020 17:36:49 +0100

---------- Forwarded message ---------
From: Stefan Israelsson Tampe <address@hidden>
Date: Tue, Jan 14, 2020 at 5:23 PM
Subject: Re: GNU Guile 2.9.9 Released [beta]
To: Mikael Djurfeldt <address@hidden>

This is how it always have been in guile, without this patch you cannot use procedure-property, use a function as a key to hash maps etc. If this patch goes you need to forbid usage
of procedures as keys to hashmap, nuke procedure properties and friends or mark it as internal to avoid luring schemers into using a faulty method. This patch improves the use of higher order functions
not risk it. For example I often classify functions into different categories and maintain this information as a property on the function via a hashmap. This is a quite natural way of programming. Without it you need
to put the procedures in a datastructure and track that datastructure that will uglify a lot of code. It is manageable but when the opposite is similarly speeded code but much nicer and enjoyable code with absolutely no risk in
higher order functionality countrary as you state (because higher order worked flawlessly before in guile and the patch is restoring that).

On Tue, Jan 14, 2020 at 5:07 PM Mikael Djurfeldt <address@hidden> wrote:
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,

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?

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

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


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