I'm not a particular fan of exhaustiveness checking. It just encourages people to write:
foo (Just 1) [x:xs] = important case foo _ _ = error "doh!" So now when the program crashes, instead of getting a precise and guaranteed correct error message, I get "doh!" - not particularly helpful for debugging. I think it's not that useful for writing personal code, but for writing production code (which you're going to ship off) it's probably important that you cover all cases. However, for that it would be much better to use a tool such as Catch (http://community.haskell.org/~ndm/catch), which actually guarantees you won't crash, rather than a simple syntactic check. As such, I think it's perfect to be included in a set of warnings, but not great to be a default. I also think that if we change our policies every time someone writes a critical blog we'll be going round in circles :-) I'm also not a fan of the overlapping patterns warning being on by default, as I often write: foo (Case1 x y z) = ... foo (Bar x) = ... foo x = error $ show ("Unhandled in foo",x) This is overlapping, and for a very good reason. Thanks Neil On Mon, May 18, 2009 at 2:18 AM, Lennart Augustsson <lenn...@augustsson.net> wrote: > The exhaustiveness checker in ghc is not good. It reports > non-exhaustive matching a bit too often and also the error messages > are often not in terms of the original source but some desugared > version. > > If those things were improved I think it should be always on. > > On Mon, May 18, 2009 at 12:53 AM, Don Stewart <d...@galois.com> wrote: >> >> I'm not sure I'd want -Wall on by default (though being -Wall clean is >> very good). But exhaustive pattern checking might well help out a lot of >> people coming from untyped backgrounds. >> >> http://ocaml.janestreet.com/?q=node/64 >> >> Ron's also wondering why exhaustive pattern checking isn't on ? >> >> Anyone know why it isn't the default? >> >> -- Don >> _______________________________________________ >> Glasgow-haskell-users mailing list >> Glasgow-haskell-users@haskell.org >> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users >> > _______________________________________________ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
