Resolving dependencies... cabal: Could not resolve dependencies: next goal: acme-left-pad (user goal) rejecting: acme-left-pad-3.0 (constraint from user target requires ==2.0) trying: acme-left-pad-2.0 next goal: base (dependency of acme-left-pad-2.0) rejecting: base-4.9.0.0/installed-4.9... (conflict: acme-left-pad => base>=4.8 && <4.9) 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.