[Haskell] IO, exceptions and error handling

Mark Carroll mark at chaos.x-philes.com
Mon Jun 14 12:03:04 EDT 2004

On Mon, 14 Jun 2004, Keith Wansbrough wrote:
> to lose referential transparency.  What is the value of
> catchExcept (show (makeExcept "E1" + makeExcept "E2")) (\x -> x)
> ?  Haskell wouldn't be "purely functional" any more.

We've already had these issues raised on haskell-cafe when I've been
wanting non-monadic synchronous exceptions. (-: The answer is that you
evaluate all branches sufficiently to discover all the exceptions raised,
and maybe have an ordering on exceptions such that you can return
"answers" deterministically (as a list of ones that occurred or
something). I'll be happy to follow discussion of this on haskell-cafe but
will be reluctant to say much that I've already said (e.g. in December
2002's "Error Handling") for fear of boring everyone silly.

-- Mark

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