On Mon, Nov 3, 2008 at 6:24 AM, Simon Marlow <[EMAIL PROTECTED]> wrote: > Jason Dagit wrote: >> >> On Wed, Oct 8, 2008 at 1:19 AM, Simon Marlow <[EMAIL PROTECTED]> wrote: >>> >>> Johannes Waldmann wrote: >>>> >>>> with 6.10, the following does not typecheck: >>>> >>>> foo `Control.Exception.catch` \ _ -> return bar >>>> >>>> Ambiguous type variable `e' in the constraint: >>>> `Control.Exception.Exception e' >>>> >>>> It is probably bad programming style anyway but what is the workaround? >>> >>> As long as you're aware that it is bad programming style. We >>> deliberately >>> didn't include an easy way to do this, because we want people to think >>> about >>> why they need to catch *all* exceptions (most of the time it's a bug). >> >> Since the above is bad form, what should I be doing? Could someone >> please provide some examples or point me at the list of exceptions >> that I can catch? What about catching multiple types of exceptions? > > Let's distinguish two kinds of exception handling:
Thanks. This helps a lot. Mind if I put it somewhere, such as on the wiki? > As for the kinds of exception you can catch, nowadays you can catch any type > that is an instance of Exception. A good place to start is the list of > instances of Exception in the docs: > > http://www.haskell.org/ghc/dist/stable/docs/libraries/base/Control-Exception.html#t%3AException > > although that only contains types defined by the base package. > > Others have commented on the backwards-compat issues, I don't have anything > to add there. Ah, but I had one more question that I don't think anyone has answered yet. That is, how to deal with multiple types of exceptions. Suppose, as a concrete example, that I was looking out for both ExitCode and PatternMatchFail exceptions. Maybe I'm being naive, but it seems like I'm in that situation again where I have to catch all and then check if fromException succeeds on either PatternMatchFile or ExitCode types. And then throw if it both give Nothing? Thanks! Jason _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
