printing of circular objects does not terminate when shown by `describe'

[felix winkelmann]

In csi, describing an object containing circular data will result in non-termination.

[Christian Kellermann]

Ok, testcases:

(define p '( a . b))
(set! (cdr p) p)
(define l (cons 'c p))

With the patch:
#;1> ,d l
circular list: c -> a -> a (circle)
#;2> ,d p
circular list: a -> a (circle)

I think, that this does ease the situation, although there might be cases where this does not do the right thing?

[Christian Kellermann]

bugfix proposal

[felix winkelmann]

Thanks! Added in e6eb2d2 (exp.).

Note thar this will still fail:

#;> (define x '(1))
#;> (set-car! x x)

[Christian Kellermann]

I am not sure about the best way to fix this. There are at least two ways I see:

1. Extend circular-list? to detect circular cars
2. Add checks for the list? and pair? cases, which would mean to either a) extend descseq and make the pair? case use that b) make a standalone check procedure and have that used also by descseq

so basically this would work the same as the code I have proposed for circular lists:
Collect all car's and check that the car's are not eq?.

[Christian Kellermann]

The circular.patch (attached) works on lists that have its car pointing somwhere inside itself as well as its cdr (and both).

[Christian Kellermann]

improved bugfix proposal

[felix winkelmann]

Excellent. Patch is applied in 82881d88cfbf6124b83952a2482efa46a7afd59d (exp.).

Thanks!

[felix winkelmann]

Milestone 4.6.0 deleted