Hi Tomas,
> : (cadr (cons 1 2))
> Segmentation fault (core dumped)
Yes, this is a known bug. In fact, it was a deliberate design decision.
There is always a trade-off between runtime-checks and performance.
PicoLisp tries to walk along the line of doing runtime checks for
typical errors, but not more than necessary.
The core dump arises because a number is accessed illegally. If you try
: (car 1)
!? (car 1)
1 -- List expected
?
the error is caught. The same happens for
: (car (cdr (1 . 2)))
!? (car (cdr (1 . 2)))
2 -- List expected
?
So those functions check their *direct* arguments, but not the whole
traversed chain. If you look at the definition of 'cadr'
any doCadr(any ex) {
any x = cdr(ex);
x = EVAL(car(x));
NeedLst(ex,x);
return cadr(x);
}
you see the check with 'NeedLst()', and then the call of the Macro 'cadr()'.
'cadr(x)' expands to x->cdr->car, and cadddr(x) to x->cdr->cdr->cdr->car.
It would be quite some overhead to expand this with a check between each
pointer dereference, which at normal program operation (if the code was
tested at least once) would never find an error.
In a nutshell, if you want to be sure to catch such errors, simply use
(car (cdr (x))) instead of (cadr x).
There are plenty of other possibilities to produce a core dump ;-)
Just try, say
: (setq a 1)
-> 1
: (a)
Segmentation fault
But I think this is acceptable in return for other advantages like
simplicity and speed.
> Is this the right place to report bugs or is there any bug tracking
> system for picolisp?
No, here is just fine. That's why we started this mailing list.
Cheers,
- Alex
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