Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: gruff (user goal)
rejecting: gruff-0.3.4, 0.3.3 (global constraint requires ==0.3.1)
trying: gruff-0.3.1
trying: bytestring-0.10.6.0/installed-236... (dependency of gruff-0.3.1)
next goal: parallel (dependency of gruff-0.3.1)
rejecting: parallel-3.2.0.6, 3.2.0.5, 3.2.0.4, 3.2.0.3, 3.2.0.2, 3.2.0.0
(conflict: gruff => parallel>=3.1 && <3.2)
rejecting: parallel-3.1.0.1, 3.1.0.0 (conflict: bytestring =>
deepseq==1.4.1.1/installed-8fb..., parallel => deepseq>=1.1 && <1.2)
rejecting: parallel-3.0.0.0, 2.2.0.1, 2.2.0.0, 2.1.0.0, 2.0.0.0, 1.1.0.1,
1.1.0.0, 1.0.0.1, 1.0.0.0 (conflict: gruff => parallel>=3.1 && <3.2)
Dependency tree exhaustively searched.