Haskell Platform Proposal: add the 'aeson' library

Michael Snoyman michael at snoyman.com
Fri Oct 11 23:15:04 UTC 2013

On Wed, Sep 18, 2013 at 10:09 AM, Simon Hengel <sol at typeful.net> wrote:

> On Wed, Sep 18, 2013 at 09:02:16AM +0200, Bas van Dijk wrote:
> > On 18 September 2013 06:30, Niklas Hambüchen <mail at nh2.me> wrote:
> > > On 18/09/13 04:02, Dan Burton wrote:
> > >> Everybody already uses, trusts, and loves aeson.
> > >
> > > There's only one thing about it that I don't trust:
> > >
> > > "Partial instances" that will call error in pure code and crash my
> program.
> > >
> > > ByteString has such an instance that simply assumes that ByteString is
> > > the same as Text, so it calls Data.Text.Encoding.decodeUtf8 on it.
> > >
> > > https://github.com/bos/aeson/issues/126
> >
> > What about settling that issue by adding documentation to the ToJSON
> > ByteString instance and the 'encode' function warning users about
> > this?
> That looks scary.  I'd either make it total or remove the instance all
> together.
> I think by now almost everybody in the Haskell community agrees that we
> do not want pure partial functions.
I don't want this issue to block inclusion of aeson. And IMO, the HP review
process shouldn't be a time to try and twist a maintainer's arm into making
a change he/she isn't interested in. That happened quite a bit on the text
package, and I don't want to see it happen on aeson as well (especially
given that Bryan would be the victim in both cases).

That said, I personally would prefer removing the ToJSON/FromJSON instances
for ByteString. We've been bitten by this in our codebases, and have
resorted to using a ByteString64 newtype wrapper, which uses base64
encoding to ensure safe roundtripping.

So: +1 from me on including aeson as-is, and if Bryan's interested in
making this change to aeson, I'd consider it a perk.

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