[Haskell-cafe] Testing invasive proposals with Hackager

AlanKim Zimmerman alan.zimm at gmail.com
Thu Jun 13 20:45:43 CEST 2013

Roman Cheplyaka has written a tool called HasFix for updating source based
on new versions of libraries.

The presentation on it is here http://ro-che.info/docs/ and the code is at

Perhaps it could be pressed into use for automatic update of historical


On Thu, Jun 13, 2013 at 6:30 PM, Maksymilian Owsianny <
maksymilian.owsianny at gmail.com> wrote:

> I was thinking about something similar some time ago, but not just
> testing but also fixing things automatically. Taking for example
> Semigroup => Monoid this would break in places where you have instance
> for Monoid but don't have instance for Semigroup. But if you have
> instance for Monoid making instance for Semigroup is straightforward:
> instance Semigroup <TypeYouAreFixing> where
>     (<>) = <copy code from mappend for that type>
> I'm still kind of new to Haskell, so I'm not sure how hard such,
> TemplateHaskell-like automagic migration tool, would be to make, but
> I feel like such a tool would be of incredible importance for the
> community. Because otherwise, without such thing, there are usually
> two ways a language can evolve:
>     1. Caring for backwards compatibility, and accumulating mistakes
>        like that over time, and becoming more and more like crap.
>     2. Making fixes that break everyones code, and because of that
>        being ignored by the industry.
> I like Haskell because it usually takes the second route, but as
> community grows it will be less and less the case. With such a tool
> you could have best of both worlds.
> Though I assume that somebody already thought of that and come to the
> conclusion that in general case you cannot make such tool because
> Gödel is a bastard that breaks everyones toys, or something along this
> lines.
> On Thu, Jun 13, 2013 at 12:54 PM, Niklas Hambüchen <mail at nh2.me> wrote:
>> On 13/06/13 18:36, Vo Minh Thu wrote:
>> > "For example, here is a run with GHC, no special options and using 4
>> > threads (note that this generally takes a long time, i.e. a few days):"
>> My builds finished in < 10 hours on an i7.
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