On Fri 24 Jun 2016 18:29, Andy Wingo <wi...@pobox.com> writes:
> 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)))))
Narrowed down:
,opt (let* ((x (list 'a))
(y (list 'a)))
(list x y))
;; ->
(let* ((x (list 'a)) (y x)) (list x y))
It's a bug in 2.0's CSE pass somehow.
Andy
