From: Alexander Asteroth <alex@soeven.de>
To: guile-user@gnu.org
Subject: letrec semantics
Date: Mon, 28 Nov 2022 09:33:54 +0100 [thread overview]
Message-ID: <87sfi379eb.fsf@soeven.de> (raw)
Dear all,
I know this topic has been discussed in the past. I found at least one
discussion in 2003 in guile-user@gnu.org which in the end referred to
even earlier discussions in comp.lang.scheme. But still I'm confused
about this and wonder if someone could help with this or point me to a
discussion that resolves the following issue.
In R5RS it sais about letrec:
>Semantics: The 〈variable〉s are bound to fresh locations
> holding undefined values, the 〈init〉s are evaluated in the
> resulting environment (in some unspecified order), each
> 〈variable〉 is assigned to the result of the corresponding
> 〈init〉, the 〈body〉 is evaluated in the resulting environmet [...]
As I (and others) understand
> scheme@(guile-user)> (letrec ((b a)(a 7)) b)
> $1 = 7
should be equivalent (of course in a new scope) to:
> scheme@(guile-user)> (define b #nil)
> scheme@(guile-user)> (define a #nil)
> scheme@(guile-user)> (set! b a)
> scheme@(guile-user)> (set! a 7)
> scheme@(guile-user)> b
> $2 = #nil
but obviously it is't. Why is b assigned to a's reference rather than
it's value in letrec? ... and would it be a correct implementation of
R5RS-letrec to return #nil from the letrec above?
Cheers,
Alex
next reply other threads:[~2022-11-28 8:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-28 8:33 Alexander Asteroth [this message]
2022-11-28 9:25 ` letrec semantics Jean Abou Samra
2022-11-30 17:23 ` Alexander Asteroth
2022-11-28 14:07 ` Taylan Kammer
2022-11-30 17:24 ` Alexander Asteroth
2022-12-01 9:30 ` Linus Björnstam
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