Re: Potential infinite loop in sb-c::array-type-upgraded-element-type with sb-kernel:union-type

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On Tue, Aug 6, 2024 at 10:36 PM Shubhamkar Ayare via Sbcl-help <
[email protected]> wrote:

> I discovered the above function calls while trying to debug a
> stuck-on-compilation issue in one of my libraries.
>
> Thanks for pointing out that this function call is not supposed to happen!
> So, the bug must lie in whatever macroexpansion and compiler macroexpansion
> my library is performing. I will debug that part.
>
> -------- Original message --------
> From: Douglas Katzman <[email protected]>
> Date: 07/08/24 00:20 (GMT+05:30)
> To: Shubhamkar Ayare <[email protected]>
> Cc: [email protected]
> Subject: Re: [Sbcl-help] Potential infinite loop in
> sb-c::array-type-upgraded-element-type with sb-kernel:union-type
>
> In both usages you are calling the function in ways that it should not be
> called by the compiler.
>
> NULL hits the member-type case and the (mapcar #'ctype-of) returns the
> same object, so it recurses on the same arg that it was called with; i.e.
> there is no base case to the recursion.
> In the second example you're just plain calling it wrong.
>
> What point are you trying to make by exercising an internal function
> incorrectly though?
>
> On Tue, Aug 6, 2024 at 2:36 PM Shubhamkar Ayare via Sbcl-help <
> [email protected]> wrote:
>
>>
>> On SBCL 2.4.7 (and also 2.4.4 and 2.4.5), the following seems to result
>> in an
>> infinite loop. It never returns despite running for 10 seconds.
>>
>>     (sb-c::array-type-upgraded-element-type (sb-kernel:specifier-type
>> '(or array null)))
>>
>> By contrast, the following returns almost immediately:
>>
>>     (sb-c::array-type-upgraded-element-type '(or array null))
>>
>> Is the difference of behavior a bug?
>>
>> Best,
>> Shubhamkar / digikar
>>
>>
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