quick report using GHC 7.10 RC3

Michael Snoyman michael at snoyman.com
Thu Mar 26 09:54:59 UTC 2015

On Thu, Mar 26, 2015 at 11:40 AM Erik Hesselink <hesselink at gmail.com> wrote:

> On Mon, Mar 23, 2015 at 6:44 AM, Mark Lentczner
> <mark.lentczner at gmail.com> wrote:
> > 7. Cabal incompatible API change
> > In particular, the api that a custom Setup.hs uses.
> > Distribution.Simple.UserHooks changed the type of a hook. It should not,
> it
> > should have added another to do what it wanted. The poblem is you can't
> use
> > CPP in Setup.hs. And so now anyone using the testHook hook is in a
> pickle:
> > Your Setup.hs can't work in both 7.10 and 7.8!
> It can, but it's a bit tricky. When this happened before, people used
> a type class with two instances, where one of them filled in a default
> argument, IIRC. I can't find the exact code now, perhaps others
> remember this better.
I wrote a blog post in June of last year[1] and was told that some of those
tricks are used to Cabal files. I also don't have a link to a real example,
but the blog post may help.


[1] http://www.yesodweb.com/blog/2014/06/evil-conditional-compile
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