[Haskell-cafe] How to catch all exceptions that could be caught?

Magicloud Magiclouds magicloud.magiclouds at gmail.com
Thu Jan 12 08:52:38 CET 2012

Thank you so much. I was always confused by what exception should I catch.

On Thu, Jan 12, 2012 at 3:49 PM, Gregory Crosswhite
<gcrosswhite at gmail.com> wrote:
> On 01/12/12 16:58, Magicloud Magiclouds wrote:
>> Yes, that is a problem. But consider my PS in original mail, I have no
>> idea what exception should I catch. Where could I get that
>> information?
> In my experience, exceptions fall into three categories.
> First, when performing IO, some functions throw an exception instead of
> returning an error code, as is the case for many of the functions in
> System.IO;  however, in these cases the exceptions that can be thrown
> are clearly documented.
> Second, when a bug in your code has caused it to reach a point where it
> can no longer proceed, such as when there is a deadlock, when there is
> an infinite loop, when you violated a precondition of a pure function by
> for example calling "head" on an empty list, etc.;  in such cases it is
> very unlikely that you would even want to catch and gracefully recover
> from them, so an exception specification would not help you very much
> anyway.
> Third, when you are running someone else's code and you want to be able
> to catch any exceptions it throws so that you can handle the error
> reporting yourself; in this case the only thing that you care about is
> whether the exception is an AsyncException or not, since if it is an
> AsyncException then you should almost certainly should just let it
> propagate up the call stack rather than dealing with it yourself.
> Incidentally, in all of these cases catching *all* exceptions is a bad
> idea unless you really know what you are doing for the reasons that
> others here have pointed out, so I apologize for misleading you with
> that suggestion.
> Cheers,
> Greg


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