---------- Původní zpráva ----------
Od: Simon Hengel <sol <at> typeful.net>
Datum: 7. 11. 2012
Předmět: Re: [Haskell-cafe] Where is the documentation on exception types kept?

Hi,

> I am trying to catch an "thread blocked on MVar indefinitely exception."  Of
> course I can use ::SomeException as explained in http://hackage.haskell.org/
> packages/archive/base/latest/doc/html/Control-Exception.html#g:3 but there
> is no explanation as to how to find the more case specific exceptions. 
> http://hackage.haskell.org/packages/archive/base/latest/doc/html/Control-
> Concurrent-MVar.html#t:MVar does not discuss exceptions at all!  Indeed, I
> don't know of any haddock pages that include descriptions of exception types
> :( :O

In this particular case it's easy:

http://hackage.haskell.org/packages/archive/base/4.6.0.0/doc/html/Control-Exception.html#t:BlockedIndefinitelyOnMVar

But in general, figuring out the exception type is not straight forward.
Personally, I think an uncaught exception should print the type of that
exception (e.g. use a derived show instance). But most of them have a
show instance that is useful for end-users.

The upcoming 1.4.0 release of Hspec will print the type of uncaught
exceptions in test cases. So if you are into BDD/TDD that might be
useful;)

Cheers,
Simon

---------- Původní zpráva ----------
Od: Albert Y. C. Lai <trebla <at> vex.net>
Datum: 7. 11. 2012
Předmět: Re: [Haskell-cafe] Where is the documentation on exception types kept?

On 12-11-07 03:36 PM, timothyhobbs <at> seznam.cz wrote:
> I am trying to catch an "thread blocked on MVar indefinitely
> exception." Of course I can use ::SomeException as explained in
> http://hackage.haskell.org/packages/archive/base/latest/doc/html/Control-Exception.html#g:3
> but there is no explanation as to how to find the more case specific
> exceptions.

In general, because Exception instances are Typeable instances, you can
get a name, and then you can use that for searches.

import Control.Exception
import Data.Typeable

main = do
aida <- try (readFile "no")
case aida of
Left (SomeException e) -> print (typeOf e)

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