--- Begin Message ---
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Subject: |
Bug in srfi-11 (?) |
|
Date: |
Mon, 18 Nov 2019 21:01:17 +0100 |
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User-agent: |
mu4e 1.2.0; emacs 26.3 |
Hi,
I was tinkering with srfi-11 and was wondering whether the following
is correct:
> scheme@(guile-user)> ,expand (let-values (((a b c) (values 1 2 3))
> ((d . e) (values 4 5)))
> (list a b c d e))
> $26 = ((@@ (srfi srfi-11) call-with-values)
> (lambda () (values 1 2 3))
> (lambda (t-1dff1b83541ce327-16e
> t-1dff1b83541ce327-16f
> t-1dff1b83541ce327-170)
> ((@@ (srfi srfi-11) call-with-values)
> (lambda () (values 4 5))
> (lambda (d . e)
> (let ((t-1dff1b83541ce327-171 d)
> (t-1dff1b83541ce327-172 e)
> (a t-1dff1b83541ce327-16e)
> (b t-1dff1b83541ce327-16f)
> (c t-1dff1b83541ce327-170))
> (list a b c d e))))))
This differs from what the comment above the macro definition claims
to expand to.
It seems like the author forgot that he matched the temporaries before
the variables in srfi-11.scm:94.
> diff --git a/module/srfi/srfi-11.scm b/module/srfi/srfi-11.scm
> index 22bda21a2..13a2ffc4d 100644
> --- a/module/srfi/srfi-11.scm
> +++ b/module/srfi/srfi-11.scm
> @@ -95,13 +95,13 @@
> (let lp ((vars (syntax vars)))
> (syntax-case vars ()
> ((id . rest)
> - (acons (syntax id)
> - (car
> + (acons (car
> (generate-temporaries (syntax
> (id))))
> + (syntax id)
> (lp (syntax rest))))
> - (id (acons (syntax id)
> - (car
> + (id (acons (car
> (generate-temporaries (syntax
> (id))))
> + (syntax id)
> '())))))
> ((id ...) ids)
> ((tmp ...) tmps))
The code "works" anyhow because the lambdas are all nested and the
inner ones capture the parameters of the outer ones.
Which got me thinking why all the messing with temporaries is
neccessary at all. Why is
> (define-syntax let-values
> (lambda (x)
> (syntax-case x ()
> ((_ (clauses ...) b0 b1 ...)
> (let lp ((clauses #'(clauses ...)))
> (if (null? clauses)
> #'(begin b0 b1 ...)
> (syntax-case (car clauses) ()
> ((args exp)
> (with-syntax ((inner (lp (cdr clauses))))
> #'(call-with-values (lambda () exp)
> (lambda args inner)))))))))))
not sufficient? I would not consider my self a Scheme expert and it
could be that I just missed something.
It would be nice if someone could verify whether this is a bug or not.
I am using Guile 2.2.6 on Guix.
Tim.
--- End Message ---
--- Begin Message ---
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Subject: |
Re: bug#38263: Bug in srfi-11 |
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Date: |
Sun, 12 Jan 2020 22:23:21 +0100 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) |
Applied to both branches. Thanks for the patch and thanks also to Mark
for the review and initial patch!
In the future, Tim, if you have larger patches, we should work out
copyright assignment paperwork. But less-than-10-line patches are fine
without. Let me know if this is of interest to you. Cheers :)
Andy
On Tue 03 Dec 2019 19:15, Tim Gesthuizen via "Bug reports for GUILE, GNU's
Ubiquitous Extension Language" <address@hidden> writes:
> Hello again,
>
> the attached patch also adds a unit test.
> I am not into how Guile is organized: Is there anything keeping us from
> adding the change?
>
> Tim.
>
> From 99d8fb795932eb92b7d5fb09115b6691f4bfe66d Mon Sep 17 00:00:00 2001
> From: Tim Gesthuizen <address@hidden>
> Date: Tue, 3 Dec 2019 18:50:37 +0100
> Subject: [PATCH] srfi-11: Do not expose variables to later clauses
>
> The current implementation of srfi-11s let-values allows later clauses
> to access and modify variables bound in earlier clauses when the clause
> is not a proper list.
>
> * module/srfi/srfi-11.scm (let-values): Fix switched variable names.
> * test-suite/tests/srfi-11.test (let-values): Add test checking that the
> variable cannot be changed in later clauses.
> ---
> module/srfi/srfi-11.scm | 2 +-
> test-suite/tests/srfi-11.test | 9 ++++++++-
> 2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/module/srfi/srfi-11.scm b/module/srfi/srfi-11.scm
> index 22bda21a2..7afac9c5f 100644
> --- a/module/srfi/srfi-11.scm
> +++ b/module/srfi/srfi-11.scm
> @@ -91,7 +91,7 @@
> (syntax (call-with-values (lambda () exp)
> (lambda (new-tmp ...) inner))))))
> ((vars exp)
> - (with-syntax ((((new-tmp . new-var) ...)
> + (with-syntax ((((new-var . new-tmp) ...)
> (let lp ((vars (syntax vars)))
> (syntax-case vars ()
> ((id . rest)
> diff --git a/test-suite/tests/srfi-11.test b/test-suite/tests/srfi-11.test
> index 40563dc18..9bfaa4300 100644
> --- a/test-suite/tests/srfi-11.test
> +++ b/test-suite/tests/srfi-11.test
> @@ -74,7 +74,14 @@
> '(unbound-variable . ".*")
> (let-values (((x) (values 1))
> ((y) (values (1+ x))))
> - #f))))
> + #f))
> +
> + (pass-if "first binding with rest invisible to second expr"
> + (let* ((a 1)
> + (b (let-values (((a . b) (values 2 3))
> + (c (begin (set! a 9) 4)))
> + (list a b c))))
> + (equal? (cons a b) '(9 2 (3) (4)))))))
>
> ;;
> ;; let*-values
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