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

Hi George, If you do not want to pattern match on `ys`, the simplest solution is to do what the GHC warning suggests you to do and use `drop 1` instead of `tail`. Another alternative is `Data.List.uncons` followed by `Data.Maybe.maybe`. Best regards, Andrew

On 20 Apr 2024, at 13:28, George Colpitts wrote:

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 mailto:george.colpitts@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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