Resolving dependencies...
cabal: Could not resolve dependencies:
[__0] trying: ghc-justdoit-0.1.0.1 (user goal)
[__1] next goal: ghc (dependency of ghc-justdoit)
[__1] rejecting: ghc-8.4.3/installed-8.4... (conflict: ghc-justdoit =>
ghc>=8.5)
[__1] trying: ghc-8.6.1
[__2] next goal: base (dependency of ghc-justdoit)
[__2] rejecting: base-4.11.1.0/installed-4.1... (conflict: ghc => base<0 &&
==4.12.*)
[__2] rejecting: base-4.12.0.0, base-4.11.1.0, base-4.11.0.0, base-4.10.1.0,
base-4.10.0.0, base-4.9.1.0, 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)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: base, ghc-justdoit, ghc