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 <george.colpitts@gmail.com> 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 <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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