Re: [Haskell-cafe] Correct way to "catch all exceptions"

Don´t tried it and probably it does not even compile, but a possibility could be along these lines: catchExcept excepts handle e= do if not . null $ filter ( \(SomeException e') -> typeOf e= typeOf e') excepts then throw e else handle e use: u= undefined excluded= [SomeException (u :: AsyncException), SomeException (u ::ArithException)] sample= expr `catchExcept` excluded $ do .... .... 2013/7/10 Erik Hesselink

Hi Michael,

We do this as well. In addition to AsyncException, we ignore BlockedIndefinitelyOnSTM, BlockedIndefinitelyOnMVar and Deadlock. I'm not sure you can ignore Timeout, since the type is not exported from System.Timeout. I'm not sure how to classify these, though. They are in some sense non-recoverable: restarting whatever the thread was doing is not the right thing to do.

Erik

...

There's a pattern that arises fairly often: catching every exception

...

by code. The naive approach is to do something like:

result <- try someCode case result of Left (e :: SomeException) -> putStrLn $ "It failed: " ++ show e Right realValue -> useRealValue

This seems perfectly valid, except that it catches a number of exceptions which seemingly should not be caught. In particular, it catches the async exceptions used by both killThread and timeout.

I think it's fair to say that there's not going to be a single function

...

solves all cases correctly, but it is a common enough situation that

On Wed, Jul 10, 2013 at 8:28 AM, Michael Snoyman wrote: thrown that people

...

need to write code that resumes work in the case of an exception that I think we need to either have some guidelines for the right approach here, or perhaps even a utility function along the lines of:

shouldBeCaught :: SomeException -> Bool

One first stab at such a function would be to return `False` for AsyncException and Timeout, and `True` for everything else, but I'm not convinced that this is sufficient. Are there any thoughts on the right approach to take here?

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- Alberto.