Using head.hackage

Alejandro Serrano Mena trupill at
Tue Sep 10 17:17:59 UTC 2019

The instructions are quite clear. Alas, when I try to reproduce the steps
using my home-build compiler (for which I mean set the `with-compiler` in
`cabal.project` to the stage2 compiler obtained by Hadrian), I get:

> cabal new-install --lib aeson
Distribution/Client/CmdInstall.hs:(361,18)-(363,72): Non-exhaustive
patterns in lambda

Do you have any idea of what I might be doing wrong?

Thanks in advance,

El mar., 10 sept. 2019 a las 12:32, Ben Gamari (<ben at>)

> Alejandro Serrano Mena <trupill at> writes:
> > Dear GHC devs,
> > As part of our work in "quick look impredicativity", we would like to
> test
> > whether any package breaks. I've read about "head.hackage" as a way to
> test
> > this fact, but I could not find any information.
> >
> > Could somebody point me in the right direction? If it does not exist yet,
> > I'll try to summarize whatever I learn in the wiki for future reference.
> >
> Hi Alejandro,
> Indeed I have a pair of yet-to-be-published blog posts intended to
> discuss exactly this. See [1] and [2]. Do let me know if you have any
> questions.
> Cheers,
> - Ben
> [1]
> [2]
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