I can confirm that the problem was that elm-repl got a stack overflow when
trying to print the value. Stupid me for not thinking about that... :(
On Saturday, 21 January 2017 03:16:57 UTC+1, Joey Eremondi wrote:
>
> But Succ shouldn't be called recursively, it should just take its
> argument, wrap it in a record, and return immediately. So Succ is getting
> called 5000 times, but never in a stack 5000 deep. (This is clearly the
> case, because if it wasn't returning, we'd never hit the continue to jump
> back to the while loop and loop again).
>
> Are you perhaps trying to print it? The print function would likely be
> recursive, and it could easily stack-overflow.
>
> On Fri, Jan 20, 2017 at 6:12 PM, GordonBGood <gordo...@gmail.com
> <javascript:>> wrote:
>
>> The code is TCO'ed but look at the data structure: the code is
>> successively calling the `Succ` function to build a successively nested
>> record structure, which overflows the stack at about 5000 recursive nests
>> in the case of the OP.
>>
>>
>> On Saturday, 21 January 2017 01:36:36 UTC+7, OvermindDL1 wrote:
>>>
>>> On Friday, January 20, 2017 at 11:17:32 AM UTC-7, mrbackend (Roy
>>> Brokvam) wrote:
>>>>
>>>> Consider:
>>>> type Nat
>>>> = Zero
>>>> | Succ Nat
>>>>
>>>>
>>>> nat : Int -> Nat
>>>> nat n =
>>>> nat_ n Zero
>>>>
>>>>
>>>> nat_ : Int -> Nat -> Nat
>>>> nat_ n curr =
>>>> if n <= 0 then
>>>> curr
>>>> else
>>>> nat_ (n - 1) (Succ curr)
>>>>
>>>> Using tail recursion, this should be stack safe in Elm (as far as I
>>>> understand). But I get a stack overflow for large values of n (>= 5000).
>>>> Is
>>>> my function really tail recursive, or might there be a bug in Elm?
>>>>
>>>
>>> It compiles into this:
>>> ```elm
>>> var _user$project$Temp1484937158714761$Succ = function (a) {
>>> return {ctor: 'Succ', _0: a};
>>> };
>>> var _user$project$Temp1484937158714761$nat_ = F2(
>>> function (n, curr) {
>>> nat_:
>>> while (true) {
>>> if (_elm_lang$core$Native_Utils.cmp(n, 0) < 1) {
>>> return curr;
>>> } else {
>>> var _v0 = n - 1,
>>> _v1 = _user$project$Temp1484937158714761$Succ(curr);
>>> n = _v0;
>>> curr = _v1;
>>> continue nat_;
>>> }
>>> }
>>> });
>>> var _user$project$Temp1484937158714761$Zero = {ctor: 'Zero'};
>>> var _user$project$Temp1484937158714761$nat = function (n) {
>>> return A2(_user$project$Temp1484937158714761$nat_, n,
>>> _user$project$Temp1484937158714761$Zero);
>>> };
>>> ```
>>> So it does look TCO'd, what is the exact stack trace that you got?
>>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "Elm Discuss" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to elm-discuss...@googlegroups.com <javascript:>.
>> For more options, visit https://groups.google.com/d/optout.
>>
>
>
--
You received this message because you are subscribed to the Google Groups "Elm
Discuss" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to elm-discuss+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
