Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: hat (user goal)
rejecting: hat-2.9.0.0, hat-2.8.0.0, hat-2.7.0.12, hat-2.7.0.11, hat-2.7.0.10,
hat-2.7.0.9, hat-2.7.0.8, hat-2.7.0.7, hat-2.7.0.6, hat-2.7.0.5, hat-2.7.0.4,
hat-2.7.0.3, hat-2.7.0.2 (constraint from user target requires ==2.7.0.1)
trying: hat-2.7.0.1
next goal: base (dependency of hat-2.7.0.1)
rejecting: base-4.9.0.0/installed-4.9... (conflict: hat => base==4.5.*)
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.