Resolving dependencies... cabal: Could not resolve dependencies: next goal: ConcurrentUtils (user goal) rejecting: ConcurrentUtils-0.4.4.0, ConcurrentUtils-0.4.2.0, ConcurrentUtils-0.4.1.0, ConcurrentUtils-0.4.0.0, ConcurrentUtils-0.3.0.0 (constraint from user target requires ==0.2.0.0) trying: ConcurrentUtils-0.2.0.0 next goal: base (dependency of ConcurrentUtils-0.2.0.0) rejecting: base-4.9.0.0/installed-4.9... (conflict: ConcurrentUtils => base>=2 && <=4) rejecting: base-4.9.0.0, base-4.8.2.0, base-4.8.1.0, base-4.8.0.0, base-4.7.0.2, base-4.7.0.1, base-4.7.0.0, base-4.6.0.1, base-4.6.0.0, base-4.5.1.0, base-4.5.0.0, base-4.4.1.0, base-4.4.0.0, base-4.3.1.0, base-4.3.0.0, base-4.2.0.2, base-4.2.0.1, base-4.2.0.0, base-4.1.0.0, base-4.0.0.0, base-3.0.3.2, base-3.0.3.1 (constraint from non-upgradeable package requires installed instance) Dependency tree exhaustively searched.