Resolving dependencies...
cabal: Could not resolve dependencies:
trying: ot-0.2.1.0 (user goal)
next goal: ghc (dependency of ot-0.2.1.0)
rejecting: ghc-8.0.1.20161018/installed-8.0... (conflict: ghc =>
binary==0.8.3.0/installed-0.8..., ot => binary>=0.5.1.1 && <0.8)
Dependency tree exhaustively searched.