On Wednesday 29 March 2006 09:49, Andrew Pimlott wrote:
If you want to write a MonadError operation that can be used with Maybe or Either, it would look like
f :: (MonadError e m, Error e) => Bool -> m Int f b = if b then return 42 else throwError (strMsg "The boolean was false.")
As long as you're happy only using Strings for your error constructs. Or you're willing to write a global construct<->String codec across all error constructs. Doesn't sound very pleasant to me.
But I see your point now about MonadFail (having throw but not catch) being perhaps preferable for this use.
My intuition is that you'd want three error related monads, Fail, Catch and Convert, to achieve what I'm after... don't know if that's a good intuition or not. :) Daniel