package 'categories' fails with HEAD

[Gabor Greif]

Hi all,

some time ago I filed:

https://github.com/ekmett/categories/issues/4

against the 'categories' library. But I cannot see what is wrong with
the code. It also builds with older GHCs (though I should re-check
with 7.8.3).

So I conjecture this is a HEAD problem in GHC HEAD. It seems weird.

Any ideas what this could be?

Cheers,

    Gabor