Resolving dependencies... cabal: Could not resolve dependencies: trying: Decimal-0.4.2/installed-7mR... (user goal) next goal: haquil (user goal) rejecting: haquil-0.1.7.5 (conflict: Decimal => base==4.10.1.0/installed-4.1..., haquil => base>=4.9 && <4.10) After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: base, Decimal, haquil Note: when using a sandbox, all packages are required to have consistent dependencies. Try reinstalling/unregistering the offending packages or recreating the sandbox.