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

[Carter Schonwald]

Respectfully I disagree.

You are pushing a breaking change to functionality in the base exception
Api without
a) demonstrating the Api is better
 b) understanding the impact on preexisting code that would needlessly
break
c) without doing a prototype outside of base to demonstrate that this
alternative is better both in terms of the underlying library complexity
and how the resulting application complexity changes.

I am voicing an opinion other readers on the libraries list have on this
matter but are too polite or wise to air this feedback publicly.

The onus is on the proposer to demonstrate validity.

Cheers
-Carter

On Friday, July 15, 2016, David Feuer <david.feuer at gmail.com> wrote:

> 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" <carter.schonwald at gmail.com
> <javascript:_e(%7B%7D,'cvml','carter.schonwald at gmail.com');>> 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 <davidleothomas at gmail.com
>> <javascript:_e(%7B%7D,'cvml','davidleothomas at gmail.com');>> wrote:
>>
>>> 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 :)
>>>
>>> On Thu, Jul 14, 2016 at 3:20 PM, Carter Schonwald
>>> <carter.schonwald at gmail.com> wrote:
>>> > At this point maybe it'd be better to write out these ideas as a
>>> library and
>>> > implement a bunch of example codes for different approaches.  Changing
>>> the
>>> > interfaces for exception handling code is subtle stuff!
>>> >
>>> >
>>> > On Jul 14, 2016 5:42 PM, "Oliver Charles" <ollie at ocharles.org.uk>
>>> wrote:
>>> >>
>>> >> data ExceptionHandler a = Rethrow | HandleException (IO a)
>>> >>
>>> >> would be my offering of paint.
>>> >>
>>> >> On Thu, Jul 14, 2016 at 9:52 PM David Feuer <david.feuer at gmail.com>
>>> wrote:
>>> >>>
>>> >>> Handle is no good because it clashes with file handles. How about
>>> >>> Reaction?
>>> >>>
>>> >>>
>>> >>> On Jul 14, 2016 1:53 PM, "Andreas Abel" <andreas.abel at ifi.lmu.de>
>>> wrote:
>>> >>>>
>>> >>>> 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" <ollie at ocharles.org.uk
>>> >>>>> <mailto:ollie at ocharles.org.uk>> wrote:
>>> >>>>>
>>> >>>>>
>>> >>>>>
>>> >>>>>     On Tue, 12 Jul 2016, 1:23 a.m. David Feuer, <
>>> david.feuer at gmail.com
>>> >>>>>     <mailto:david.feuer at 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 at 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 at gu.se
>>> >>>> http://www2.tcs.ifi.lmu.de/~abel/
>>> >>
>>> >>
>>> >> _______________________________________________
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>>> >>
>>> >
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>>> >
>>>
>>
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