Hi Henning, Thus quoth Henning Thielemann on Wed Nov 29 2017 at 11:04 (+0100):
Occasionally I have multiple implementations of the same task and want to choose one quickly but statically. I do not want to out-comment unused branches because they shall still be type checked. So far I used this scheme:
case 0::Int of 0 -> putStrLn "A" 1 -> putStrLn "B" _ -> putStrLn "C"
Maybe you can factor out the implementations of different branches into separate functions, like in: case 0 :: Int of 0 -> putStrLn "A" 1 -> handleOne1 where handleOne1 :: Int -> IO () handleOne1 = putStrLn "B" handleOne1 :: Int -> IO () handleOne2 = putStrLn "C" This should keep the typechecking.
With ghc-8.0.2 and ghc-8.2.2 I get these warnings:
RedundantCase.hs:4:7: warning: [-Woverlapping-patterns] Pattern match is redundant In a case alternative: 0 -> ...
RedundantCase.hs:5:7: warning: [-Woverlapping-patterns] Pattern match is redundant In a case alternative: 1 -> ...
I thought that "redundant" means that the first two cases overlap with '_'. But if I replace '_' by '2' I get not only the non-exhaustive patterns warning but an additional redundancy warning on pattern '2'.
Is there a nice way to tell GHC that the unused branches are intended, without generally disabling overlapping patterns warning?
To me, you are creating overlapping patterns in the case statements, so having unused branches and _not_ having warnings about them kind of breaks the point of this type of warning (personal opinion). Now, depending on the localisation of alternative branches, you may want to use per-file preprocessor directives to disable the warning. -- Sergiu
I mean, this one does not provoke any warnings:
if True then putStrLn "X" else putStrLn "Y"
but is limited to two branches. _______________________________________________ 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.