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

[George Colpitts]

Thanks for everybody's replies

To give more context the original code from Ch. 12 of Bird's *Thinking
Functionally with Haskell* was:


let (xs, ys) = break (== ch) str in

         if null ys then [] else [(xs, tail ys)])

I replaced it with

let (xs, ys@(_ : t)) = break (== ch) str in

         if null ys then [] else [(xs, t)])

On Tue, Apr 16, 2024 at 10:51 AM George Colpitts <george.colpitts at gmail.com>
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?
>
> Cheers
> George
>
>
>
>
>
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