[Haskell-cafe] Control.Exception try and catch

[Mads Lindstrøm]

Hi

From
http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Control-Exception.html#3

"... The difference between using try and catch for recovery is that in
catch the handler is inside an implicit block (see "Asynchronous
Exceptions") which is important when catching asynchronous
exceptions ..."

However, 'try' is implemented by calling catch
http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/src/Control-Exception-Base.html#try:

try :: Exception e => IO a -> IO (Either e a)
try a = catch (a >>= \ v -> return (Right v)) (\e -> return (Left e))

Thus, I wonder, why do 'try' not "inherit" the implicit block mentioned above?

Looking at catch:

catch   :: Exception e
        => IO a         -- ^ The computation to run
        -> (e -> IO a)  -- ^ Handler to invoke if an exception is raised
        -> IO a
catch io h = H'98.catch  io  (h . fromJust . fromException . toException)


I see no call to 'block'. But maybe it is hidden in H'98.catch? And is H'98.catch == Prelude.catch ?

/Mads