I actually meant relax the haskell 98 spec in the quite literal sense of changing the spec to allow for the set of exceptions to be undefined.
The set of exceptions is already undefined. The IOError type is deliberately abstract (i.e., you can't see the constructors) so that the set of exceptions can be extended. (It would have been more convenient if you could see the constructors so that you could use pattern matching but making it extensible won out over convenience.) But, whatever exception is used, changing the haskell98 spec so that catch (print (1/0)) print is not equal to bottom (as in the current spec) is a pretty big step. I helped design non-determinstic exceptions and I still think the idea is a pretty radical idea that needs more discussion and more experience before it is added to the language. -- Alastair Reid ps In case it sounds like I've changed my mind about non-deterministic exceptions. This is not so - I continue to believe that languages without exception handling are useless toys (however beautiful) and that ND-exceptions are the only viable way of adding exceptions to Haskell. What I'm saying is that I'm not sure that a concensus exists and that there may be worthwhile minor variations on the idea that should be explored.