Resolving dependencies...
cabal: Could not resolve dependencies:
trying: ghc-proofs-0.1.1 (user goal)
next goal: ghc (dependency of ghc-proofs-0.1.1)
rejecting: ghc-8.0.2/installed-8.0... (conflict: ghc-proofs => ghc>=8.2 &&
<8.4)
Dependency tree exhaustively searched.