When I encounter a segfault, it is usually caused by recursion depth being
over some kind of limit.
In your code, the 'aux' function is defined but never called. Here is a
fixed version:
fun
{a: t@ype}
brauntest1 (t0: tree a): bool =
let exception Negative of ()
fun aux (t0: tree a): bool =
case+ t0 of
| tree_nil () => true
| tree_cons (tl, _, tr) =>
let val szl = size<a> (tl)
val szr = size<a> (tr)
in
if abs (szl - szr) > 1 then $raise Negative ()
else aux(tl) andalso aux(tr)
end
in
try aux(t0) with ~Negative () => false
end
On Thu, Aug 20, 2020 at 6:46 AM Timmy Jose <zoltan.j...@gmail.com> wrote:
>
>
> Hi,
>
> I have a variation of the Braun Tree test (where the size of the left and
> right subtrees differ by at most 1 at every level) from the tutorials, and
> this one, for some reason gives a segmentation fault.
>
> Here is the snippet:
>
> fun
> {a: t@ype}
> brauntest1 (t0: tree a): bool =
> let exception Negative of ()
> fun aux (t0: tree a): bool =
> case+ t0 of
> | tree_nil () => true
> | tree_cons (tl, _, tr) =>
> let val szl = size<a> (tl)
> val szr = size<a> (tr)
> in
> if abs (szl - szr) > 1 then $raise Negative ()
> else brauntest1<a> (tl) andalso brauntest1<a> (tr)
> end
> in
> try brauntest1 (t0) with ~Negative () => false
> end
>
> And here is the output from `lldb` (gdb has some code-signing issues on
> macOS).
>
> $ lldb braun
> (lldb) target create "braun"
> Current executable set to 'braun' (x86_64).
> (lldb) r
> Process 28137 launched: '<path elided>/braun' (x86_64)
> Process 28137 stopped
> * thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
> (code=2, address=0x7ffeef3fff68)
> frame #0: 0x0000000100001577 braun`brauntest1_3__3__1 + 39
> braun`brauntest1_3__3__1:
> -> 0x100001577 <+39>: callq 0x100001c3a ; symbol stub for:
> setjmp
> 0x10000157c <+44>: testl %eax, %eax
> 0x10000157e <+46>: je 0x1000015de ; <+142>
> 0x100001580 <+48>: movq 0xb31(%rip), %rcx ;
> my_atsexnframe_getref.my_atsexnframe
> Target 0: (braun) stopped.
> (lldb)
>
> Anybody seen this before, or have an idea what might be going wrong?
>
> Thanks!
>
> Timmy
>
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