APPLY does not terminate on a circular list

[pclouds]

This is a mirror of ashinn/chibi-scheme#629. While chibi segfaults, Gauche runs forever.

(define x '#0=(a . #0#))
(apply list x)

I looked at the backtrace with gdb and it looks like when GAUCHE_LAZY_PAIR is on, check_arglist_tail_for_apply() does not handle circular list correctly. The other version, which uses Scm_Length(), does handle it and terminates with

*** ERROR: improper list not allowed: #0=(a . #0#)

PS. Gauche cannot be compiled with GAUCHE_LAZY_PAIR set to zero anymore (undefined symbols). Might as well simplify the code and get rid of non-lazy code paths.

[lassik]

Thanks a lot for testing these cases! It would be really neat to have a survey of how the primitives in different Scheme implementations handle circular lists. schemedoc/surveys?

[pclouds]

This is a very specific case, I don't think worth surveying. Though if you do, maybe coordinate with John, his wg2 repo tracks which scheme supports what feature for a lot of schemes and features.

[lassik]

maybe coordinate with John

Definitely. With the docker containers we could even do a simple framework for automated test cases. Send some input to the REPL, expect a particular set of outputs and record the results.

[shirok]

Good catch. Fix pushed.

We still don't detect if the argument is an infinite lazy list---in which case, the process eventually exhaust memory. But actually, we don't need to realize the lazy list entirely; we only need up to the number of required arguments. That'll be another task.

[pclouds]

Wow. It's good that I reported instead of attempting to fix myself. I didn't see all that. Since lazy list problem is already tracked, I'll close this one. Thanks!