Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: concurrent-extra (user goal)
rejecting: concurrent-extra-0.7.0.9, 0.7.0.8, 0.7.0.7, 0.7.0.6, 0.7.0.5,
0.7.0.4, 0.7.0.3, 0.7.0.2, 0.7.0.1, 0.7, 0.6.0.1 (global constraint requires
==0.6)
trying: concurrent-extra-0.6
next goal: base (dependency of concurrent-extra-0.6)
rejecting: base-4.8.1.0/installed-4f7... (conflict: concurrent-extra =>
base>=3 && <4.4)
rejecting: base-4.8.1.0, 4.8.0.0, 4.7.0.2, 4.7.0.1, 4.7.0.0, 4.6.0.1, 4.6.0.0,
4.5.1.0, 4.5.0.0, 4.4.1.0, 4.4.0.0, 4.3.1.0, 4.3.0.0, 4.2.0.2, 4.2.0.1,
4.2.0.0, 4.1.0.0, 4.0.0.0, 3.0.3.2, 3.0.3.1 (global constraint requires
installed instance)
Dependency tree exhaustively searched.