Dialyzer: Cons will produce an improper list since its 2nd argument is none()

[Jesper Eskilson]

Ah, my question wasn't why the error occurs in the first place, but rather
an inquiry if dialyzer oughtn't formulate the error a bit differently. :)


On Fri, Feb 14, 2020 at 1:54 PM Fernando Benavides <elbrujohalcon@REDACTED>
wrote:

> I think what's happening in this case is this…
> Dialyzer sees your code (using cons for the list) as…
>
> main() -> [ #foo{x = 0} | [#foo{x = false} | []] ].
>
> It then detects the third warning from your email (namely, that you're
> using *false* for something that should be an *integer*):
> foo.erl:9: Record construction
>           #foo{x :: false} violates the declared type of field x ::
>           integer()
> Therefore, the type of that second part of the list ([#foo{x = false} |
> []]) will be *none()*.
> And that leads dialyzer to complain with the second warning that you see…
> foo.erl:8: Cons will produce an improper list since its 2nd argument is
>           none()
> Which, in time, produces the first warning…
> foo.erl:7: Function main/0 has no local return
>
> Hope this helps.
>
> On Fri, Feb 14, 2020 at 1:45 PM Jesper Eskilson <
> jesper.eskilson@REDACTED> wrote:
>
>> Hi,
>>
>> When dialyzer analyzes this program:
>>
>>
>> -module(foo).
>> -export([main/0]).
>> -record(foo, {x :: integer()}).
>> main() ->
>>   [ #foo{x = 0},
>>     #foo{x = false} ].
>>
>>
>> it says:
>>
>> foo.erl:7: Function main/0 has no local return
>> foo.erl:8: Cons will produce an improper list since its 2nd argument is
>>           none()
>> foo.erl:9: Record construction
>>           #foo{x :: false} violates the declared type of field x ::
>>           integer()
>>
>>
>> It seems like dialyzer assumes that any cons with second argument not
>> being a list will produce an improper list, but shouldn't it treat "none()"
>> differently?
>>
>> Is this a bug in dialyzer, or a feature whose usefulness I am unable to
>> grasp?
>>
>> --
>>
>> *Jesper Eskilson*
>> Senior Software Engineer
>> Kred Core
>> +46-72-855-8421
>>
>> Klarna Bank AB (publ)
>> Sveavägen 46, 111 34 Stockholm
>> Tel: +46 8 120 120 00 <+46812012000>
>> Reg no: 556737-0431
>> klarna.com
>>
>>
>
> --
>
> <https://about.me/elbrujohalcon?promo=email_sig&utm_source=product&utm_medium=email_sig&utm_campaign=gmail_api&utm_content=thumb>
> Brujo Benavides
> about.me/elbrujohalcon
> <https://about.me/elbrujohalcon?promo=email_sig&utm_source=product&utm_medium=email_sig&utm_campaign=gmail_api&utm_content=thumb>
>


-- 

*Jesper Eskilson*
Senior Software Engineer
Kred Core
+46-72-855-8421

Klarna Bank AB (publ)
Sveavägen 46, 111 34 Stockholm
Tel: +46 8 120 120 00 <+46812012000>
Reg no: 556737-0431
klarna.com
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