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 <gordonbg...@gmail.com> 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?
>>
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