This is pretty trivial, I'll self-accept in a few days.
1 patch for repository darcs-unstable@darcs.net:screened:
patch 269ebad5f4a47b4da93c3c216a1d874e0070caff
Author: Ganesh Sittampalam <ganesh@earth.li>
Date: Sat Apr 15 00:38:13 BST 2017
* remove some impredicativity in the test harness
Impredicativity is not reliable/supported from GHC version to version
and this case has stopped working in GHC 8.0.