Re: Discussion: add more idiomatic versions of catchJust and/or handleJust

You are very welcome to do so if you don't think further discussion will be useful. Those who feel otherwise may continue to discuss it. On Jul 15, 2016 9:23 AM, "Carter Schonwald" wrote:

Again, at this juncture it sounds like effort would be better spent first writing out an alternative userland lib to understand these design ideas / articulate their impact better

On Friday, July 15, 2016, David Thomas wrote:

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I kinda like "ExceptionDisposition" for the type, no particular ideas on the constructors. Offered only in the spirit of tossing out ideas - feel free to ignore me if it's not helpful :)

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At this point maybe it'd be better to write out these ideas as a

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implement a bunch of example codes for different approaches. Changing

On Thu, Jul 14, 2016 at 3:20 PM, Carter Schonwald wrote: library and the

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interfaces for exception handling code is subtle stuff!

On Jul 14, 2016 5:42 PM, "Oliver Charles" wrote:

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data ExceptionHandler a = Rethrow | HandleException (IO a)

would be my offering of paint.

On Thu, Jul 14, 2016 at 9:52 PM David Feuer

wrote:

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Handle is no good because it clashes with file handles. How about Reaction?

On Jul 14, 2016 1:53 PM, "Andreas Abel"

wrote:

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Maybe rather

data Handle a = Rethrow | Handle (IO a)

!? On 14.07.2016 19:12, David Feuer wrote: > > That makes sense, I guess. Something like > > data Handle a = Rethrow | Catch (IO a) > > I suppose? My names are awful though. > > > On Jul 14, 2016 12:56 PM, "Oliver Charles" mailto:ollie@ocharles.org.uk> wrote: > > > > On Tue, 12 Jul 2016, 1:23 a.m. David Feuer, <

david.feuer@gmail.com

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> mailto:david.feuer@gmail.com> wrote: > > The catchJust and handleJust functions seem a bit weird and > unidiomatic. > > catchJust > :: Exception e > => (e -> Maybe b) -- ^ Predicate to select > exceptions > -> IO a -- ^ Computation to run > -> (b -> IO a) -- ^ Handler > -> IO a > catchJust p a handler = catch a handler' > where handler' e = case p e of > Nothing -> throwIO e > Just b -> handler b > > This takes two functions and then puts them together. I would > think the more natural API would be > > catchMaybe :: Exception e => IO a -> (e -> Maybe (IO a)) -> IO > a > catchMaybe m handler = catch m handler' where > handler' e = fromMaybe (throwIO e) (handler e) > > A point don't feel super strongly about, but feel I should raise, > is > that Nothing seems to be somewhat confusing. catchJust > (\FileNotFound -> Nothing) seems to suggest that if FileNotFound > occurs then nothing will happen, that is - the exception is > ignored. > However, that is not the case, rather than Nothing happening > something certainly happens - an exception is (re)thrown! > > Whether or not this confusion is likely to happen in practice I > don't know, but it suggests a type isomorphic to Maybe is a better > fit. > > Ollie > > > > _______________________________________________ > Libraries mailing list > Libraries@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries >

-- Andreas Abel <>< Du bist der geliebte Mensch.

Department of Computer Science and Engineering Chalmers and Gothenburg University, Sweden

andreas.abel@gu.se http://www2.tcs.ifi.lmu.de/~abel/

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