On Mar 14, 2007, at 9:33 AM, Simon Marlow wrote:
ajb@spamcop.net wrote:
6. throwDyn 7. ioError and catch
Since deprecating throwDyn was mentioned, I should say that the plan I've had in mind has been to merge (6) and (7) by using the Exception class:
http://hackage.haskell.org/cgi-bin/haskell-prime/trac.cgi/wiki/ ExtensibleExceptions http://www.haskell.org/~simonmar/papers/ext-exceptions.pdf
So there would be just one throw & catch, and you would be able to use them with arbitrary types. The scheme suggested in the paper is not completely satisfactory, and various people have suggested ways to simplify it, so it needs some reworking before I'd call it a proposal though.
Just to clarify something I've seen mentioned: throwDyn is *not* tied to the IO monad, since it has type Typeable ex => ex -> a. However, you can only catch it in the IO monad. So you should think of it as a version of 'error' that you can use with something other than String.
Since I made the comment, I'll clarify. What I meant is just what you said: error _recovery_ is tied to the IO monad. The ErrorDynT proposal I made was a way to get some of the benefits of throwDyn and still be able to have error recovery in non-IO code.
Cheers, Simon
Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG