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

[Henning Thielemann]

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)]