On Fri 13 Nov 2015 08:57, Zefram <zef...@fysh.org> writes:
> With guile 2.0.11:
>
> scheme@(guile-user)> (use-modules (ice-9 control))
> scheme@(guile-user)> (list 'a (let/ec ae (list 'b (let/ec be (be 2)))))
> $1 = (a (b 2))
> scheme@(guile-user)> (list 'a (let/ec ae (list 'b (let/ec be (ae 2)))))
> $2 = (a (b 2))
> scheme@(guile-user)> (list 'a (let/ec ae (list 'b (ae 2))))
> $3 = (a 2)
>
> The middle of these three cases is wrong: it attempts to invoke the outer
> escape continuation, but only goes as far as the target of the inner one,
> which it isn't using. It therefore produces the same result as the first
> case, which invokes the inner escape continuation. It ought to behave
> like the third case, which shows that the outer escape continuation can
> be successfully invoked when the unused inner continuation is not present.
This is a compiler bug in 2.0:
scheme@(guile-user)> ,optimize (list 'a (let/ec ae (list 'b (let/ec be (ae
2)))))
$2 = (list 'a
(let ((tag (list 'let/ec)))
(call-with-prompt
tag
(lambda ()
(list 'b
(let ((tag-1 tag)) ;; <<<< here is the bug
(call-with-prompt
tag-1
(lambda () (abort-to-prompt tag 2))
(lambda (_ . results) (@apply values results))))))
(lambda (_ . results) (@apply values results)))))
In master:
scheme@(guile-user)> ,optimize (list 'a (let/ec ae (list 'b (let/ec be (ae
2)))))
$1 = (list 'a
(let ((tag (list 'let/ec)))
(call-with-prompt
tag
(lambda ()
(list 'b
(let ((tag-1 (list 'let/ec)))
(call-with-prompt
tag-1
(lambda () (apply abort tag 2 '()))
(lambda (_ . results) (apply values results))))))
(lambda (_ . results) (apply values results)))))
Weird stuff!
Andy
