Resolving dependencies...
cabal: Could not resolve dependencies:
[__0] next goal: ehlo (user goal)
[__0] rejecting: ehlo-0.1.0.0 (conflict: requires GHC2021)
[__0] fail (backjumping, conflict set: ehlo)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: ehlo