Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: haskell-docs (user goal)
rejecting: haskell-docs-4.2.7 (constraint from user target requires ==4.2.6)
trying: haskell-docs-4.2.6
next goal: ghc (dependency of haskell-docs-4.2.6)
rejecting: ghc-8.0.1.20161018/installed-8.0... (conflict: haskell-docs =>
ghc>=7.2 && <7.11)
Dependency tree exhaustively searched.