aeson and dlist in HP 2013.4.0.0

[Don Stewart]

Indeed, avoiding expensive instances was part of the design
On Nov 18, 2013 5:21 PM, "Joachim Breitner" <mail at joachim-breitner.de>
wrote:

> Hi,
>
> Am Montag, den 18.11.2013, 10:04 +0200 schrieb Sean Leather:
> > * Maintenance and development taken over by Sean Leather
> > * Migrate repository from http://code.haskell.org/~dons/code/dlist/ to
> >   https://github.com/spl/dlist
> > * Add `Eq`, `Ord`, `Read`, `Show`, `Alternative`, `Foldable`,
> `Traversable`
> >   instances
>
> Given that the point of dlist is to speed up code where lists are
> insufficient, would it make sense to only provide those instances that
> can be implemented without converting to and from lists?
>
> If there are instances that cannot be implemented idiomatically with
> dlists, maybe they should be left out, to signal the user that he will
> not get the benefits of DLists for these.
>
> In particular, it seems that the Show instance could be improved.
> Currently it says
>           showsPrec p dl = showParen (p > 10) $
>             showString "fromList " . shows (toList dl)
> i.e. goes via a list. But this is constructing a ShowS (which is String
> -> String) value, i.e. another difference list. Shouldn’t it be possible
> to stay in the world of difference lists when implementing this?
>
> (Or maybe I’m overly worried, and I admit that I did not run benchmarks
> so far.)
>
> Greetings,
> Joachim
>
> --
> Joachim “nomeata” Breitner
>   mail at joachim-breitner.de • http://www.joachim-breitner.de/
>   Jabber: nomeata at joachim-breitner.de  • GPG-Key: 0x4743206C
>   Debian Developer: nomeata at debian.org
>
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