[Haskell-cafe] Help using catch in 6.10

[Martijn van Steenbergen]

Hi Victor,

You now need to specify the exact type of the exception you wish to 
catch. For example, to catch any exception:

action `catch` (\(e :: SomeException) -> handler)

For more information, see:

http://www.haskell.org/~simonmar/papers/ext-exceptions.pdf

HTH,

Martijn.




Victor Nazarov wrote:
> Hello, cafe.
> 
> I whant to switch to GHC 6.10
> 
> My application compiled fine with 6.8.3, but after switchin to 6.10,
> I've got errors about usage of catch function:
> 
> Main.hs:165:14:
>     Ambiguous type variable `e2' in the constraint:
>       `Exception e2' arising from a use of `catch' at Main.hs:165:14-38
>     Probable fix: add a type signature that fixes these type variable(s)
> 
> Main.hs:261:17:
>     Ambiguous type variable `e' in the constraint:
>       `Exception e' arising from a use of `handle' at Main.hs:261:17-118
>     Probable fix: add a type signature that fixes these type variable(s)
> 
> Relevant places in code are:
> 
> ...
>          getNSteps f =
>            do text <- get entryNSteps entryText
>               catch (readIO text >>= f) $ \_e ->
>                 do msgBox (Just window) [] MessageWarning ButtonsOk $
> "Число шагов указано неверно: " ++ show text
>                    return ()
> ...
> loadData :: IO ([Term], Map.Map String Term)
> loadData =
>   do examples <- handle (\_e -> msgBox Nothing [] MessageWarning
> ButtonsOk "Ошибка чтения файла примеров" >> return []) $
>        do examplesLines <- fmap lines $ readFile "examples.txt"
>           let parsings :: [Term]
>               parsings = concatMap (fromEither . parse) examplesLines
>               parse :: String -> Either ParseError Term
>               parse = Parsec.parse (Lambda.parser >>= \t -> skipMany
> space >> eof >> return t) ""
>               fromEither :: Either ParseError Term -> [Term]
>               fromEither = either (const []) (\t -> [t])
>           return parsings
> ...
> 
>