On 15 Jan 2008, at 7:54 PM, Adam Smyczek wrote:
On Jan 15, 2008, at 7:34 PM, Brandon S. Allbery KF8NH wrote:
On Jan 15, 2008, at 22:05 , Adam Smyczek wrote:
Ups, resend, first response did not make into the list. On Jan 14, 2008, at 9:33 PM, Brandon S. Allbery KF8NH wrote:
On Jan 15, 2008, at 0:28 , Adam Smyczek wrote:
It's probably a trivial question, but I cannot figure out how to implement the catchError function in:
instance MonadError String Shell where throwError = error . ("Shell failed: "++) catchError l h = ???
Take a look at Control.Exception.catch for starters.
No, did not help and going over the source code of Control.Monad.Error did not help as well. Does someone have other tips for me?
Perhaps you could explain what you're looking for? Your typeclass doesn't tell us anything about the semantics.
The type declaration:
newtype Loader a = Loader { load :: ErrorT String IO a } deriving (Functor, Monad, MonadIO)
instance MonadError String Loader where throwError = error . ("Error: " ++)
I don't think this is what you want; you're throwing away the benefit of using ErrorT. You probably want throwError = Loader . throwError
l `catchError` h = ??? how do I implement this ???
l `catchError` h = Loader (load l `catchError` load . h) jcc