Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: opencv-extra (user goal)
rejecting: opencv-extra-0.2.0.0 (conflict: requires pkg-config package
opencv>=3.0.0, not found in the pkg-config database)
rejecting: opencv-extra-0.1.0.0, opencv-extra-0.0.0.1, opencv-extra-0.0.0.0
(constraint from user target requires ==0.2.0.0)
Dependency tree exhaustively searched.