Re: [Haskell-cafe] Error handling package

20 Oct 2009


      On Tue, Oct 20, 2009 at 3:12 PM, Michael Snoyman  wrote:
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On Tue, Oct 20, 2009 at 11:04 AM, Nicolas Pouillard
 wrote:
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On Sun, Oct 18, 2009 at 9:45 PM, Michael Snoyman 
wrote:
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While working on the next release of data-object, I wanted to represent
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About the name Attempt, I think that 'Outcome' would be a better name.
The problem with a name like "Outcome" is that it doesn't really imply the
possibility of failure, simply that we are wrapping of the result for some
reason.
I don't see why, the outcome of an action could be either a success or
a failure.
Even if the only *desired* outcome is success.
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2) Are there any other FromAttempt instances I should provide out of the
box?
None that I see.
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3) I was considering adding specialized versions of the fromAttempt
function, ie ioFromAttempt, maybeFromAttempt. Thoughts?
It is a bit long to spell.
True, but it can be more convenient than giving explicit type signatures.
The main reason this might come up would be regarding the (Either String)
and (Either SomeException) instances.
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4) Should I follow the naming scheme attemptJoin, attemptLookup, etc, or
just call the functions join, lookup and force people to import the
module
qualified?
A nice alternative would be to make a Data.Attempt.Extra (or a better
name) which
would be imported qualified.
I like. The only other name I can think of right now is Data.Attempt.Helper,
but that's just painting the bike shed.
I also prefer Helper.
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5) Any other suggestions for attempt functions? I've considered
head/tail/etc.
Why not, maybe the 'safe' package should be of some inspiration.
Once they're all in their own module, I don't see a problem adding as many
as possible.
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attempt :: (forall e. Exception e -> b) -> (a -> b) -> Attempt a -> b
I was trying to more model it after fromMaybe, but instead just ended up
with something ugly. I'm going to rewrite attempt using this type signature
and then add fromAttempt as well.
Fine, fromAttempt should follow fromMaybe

fromAttempt :: (forall e. Exception e -> a) -> Attempt a -> a
fromAttempt f a = attempt f id a

Regards,

-- 
Nicolas Pouillard
http://nicolaspouillard.fr