To deal with "amigous type variable 'e'", I often write the codes like:
handle (\e@SomeException{} -> print e) (5 `div` 0)
and IIRC, the base-4.0 initially released with GHC 6.10.1, introduced
this exceptions. It enables us to specify which exception should be
caught and define types of exceptions what you want. And I hear this
is based on the paper
http://www.haskell.org/~simonmar/papers/ext-exceptions.pdf
On Wed, Oct 21, 2009 at 6:29 PM, Michael Mossey
The examples in the "error handling" chapter (19) of RWH don't run under GHC 6.10.
For instance, an example might be
main = handle (\_ -> putStrLn "error") (print $ 5 `div` 0)
Trying to load this results in "amigous type variable 'e' in the constraint: 'Exception e' arising from a use of 'handle' etc etc.
I was able to fix this via the ludicrously complex:
main2 = (handle :: (SomeException -> IO ()) -> IO () -> IO ()) (\_ -> putStrLn "Error calculating result") (print $ 5 `div` 0)
Is there a more concise way to use "handle", or can someone point me to a tutorial that might explain the changes in 6.10 and in a general way how to get the RWH examples to run?
Thanks, Mike _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe