Resolving dependencies...
cabal: Could not resolve dependencies:
[__0] trying: graphmod-plugin-0.1.0.0 (user goal)
[__1] next goal: ghc (dependency of graphmod-plugin)
[__1] rejecting: ghc-8.4.3/installed-8.4..., ghc-8.4.3, ghc-8.4.1, ghc-8.2.2,
ghc-8.2.1 (conflict: graphmod-plugin => ghc>=8.6)
[__1] fail (backjumping, conflict set: ghc, graphmod-plugin)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: graphmod-plugin, ghc