[Haskell-cafe] ghc should be able to deduce correct use of partial functions and not give a warning in such cases

[Ivan Perez]

Wouldn't you have to be able to inline null and tail to be able to say that
this use of tail is not partial? If null and tail "live" in a different
library, is there much that you can do?

Thanks,

Ivan

On Tue, 16 Apr 2024 at 07:58, George Colpitts <george.colpitts at gmail.com>
wrote:

> Hi Henning,
>
> Thanks for the quick response!
> Yes, that's basically how I fixed it but I really don't want to have to do
> that since the code is correct. Not a big deal but may be irritating to
> beginners or large projects that want to eliminate warnings. Do you think
> an ER would be rejected ? If I remember correctly there is already
> detection of incomplete pattern matching that is ok and in such cases
> warnings are omitted. This would be similar to that.
>
> Cheers,
> George
>
>
> On Tue, Apr 16, 2024 at 11:46 AM Henning Thielemann <
> lemming at henning-thielemann.de> wrote:
>
>>
>> On Tue, 16 Apr 2024, George Colpitts wrote:
>>
>> > ghc should be able to deduce correct use of partial functions and not
>> give a warning in such cases, e.g.
>> > in 9.8.2
>> >
>> >      if null ys then [] else [(xs,tail ys)])
>> >
>> > gets a warning
>> >
>> >       warning: [GHC-63394] [-Wx-partial]
>> >
>> > but it is clear that this use of tail will never be a problem so IMHO
>> that line of code should not get a
>> > warning.
>> >
>> > Does anybody know if there is a plan or enhancement request to
>> eliminate such warnings?
>>
>>
>> I would just use good old pattern matching:
>>
>> case ys of
>>     [] -> []
>>     _:zs -> [(xs,zs)]
>
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