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

The clearest way that I know to write that code fragment is case break (== ch) str of (_,[]) -> [] (xs,(_:ys)) -> [(xs,ys)] It's one line longer, but there are no warnings and NO SURPRISES for the reader. The version that matches on (_:_) before testing whether that's possible surprised me mightly. Confused me, even. On Sun, 21 Apr 2024 at 00:29, 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 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

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.