[Haskell-cafe] Hiding functions

[Bayley, Alistair]

What is wrong with creating your own catch and throw with different names?
e.g.

  data MyException = MyException ...
    deriving (Typeable, Show)

  catchMyEx :: IO a -> (MyException -> IO a) -> IO a
  catchMyEx = catchDyn
  throwMyEx :: MyException -> a
  throwMyEx = throwDyn

> But there might be code that uses 'throw' and doesn't really 
> care which one is used, and it would be nice to just modify 
> the import line and be done with it.

Can you expand on this? (more example code?) If you want to throw your own
exceptions, then you must use throwDyn/catchDyn, so you have to use
something other than catch/throw anyway.

Alistair.


> -----Original Message-----
> From: Lyle Kopnicky [mailto:lists at qseep.net] 
> Sent: 12 August 2004 20:23
> To: Haskell Cafe
> Subject: [Haskell-cafe] Hiding functions
> 
> Hi all,
> 
> I'm working on a program that uses my own brand of 
> exceptions, and I created two functions called 'throw' and 
> 'catch'.  In order for this to work, I hide the Prelude 
> 'catch' in my module, called 'Cont.hs'.  Thus:
> 
> module Cont where
> import Prelude hiding (catch)
> ...
> throw = ...
> catch = ...
> 
> This works hunky-dory until I create another file that 
> imports Cont.  I get a conflict when I use 'catch', so I have 
> to  hide the Prelude one again:
> 
> import Prelude hiding (catch)
> import Cont
> ...
> ... throw ...
> ... catch ...
> 
> So I'm a bit annoyed by this 'propagation' of hiding clauses. 
>  Then I created a new file,  that redefined throw:
> 
> module ResumableExceptions where
> import Cont hiding (throw)
> import qualified Cont (throw)
> ...
> throw = ... Cont.throw ...
> 
> Finally, I created a file using ResumableExceptions:
> 
> import Cont hiding (throw)
> import ResumableExceptions
> ...
> ... throw ...
> 
> If I wanted to also use 'catch' I'd have to hide that from 
> the Prelude as well.
> 
> I can't use type classes to solve this problem, because the 
> types of the two 'throw' functions are different.
> 
> Perhaps I should just make up new names for these things, eh? 
>  But there might be code that uses 'throw' and doesn't really 
> care which one is used, and it would be nice to just modify 
> the import line and be done with it.
> 
> Any opinions?
> 
> Thanks,
> Lyle

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