Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: ipopt-hs (user goal)
rejecting: ipopt-hs-0.5.1.0 (constraint from user target requires ==0.5.0.0)
rejecting: ipopt-hs-0.5.0.0 (conflict: requires pkg-config package ipopt-any,
not found in the pkg-config database)
rejecting: ipopt-hs-0.4.2.0, ipopt-hs-0.4.0.1, ipopt-hs-0.4.0.0,
ipopt-hs-0.3.0.0, ipopt-hs-0.2.0.0, ipopt-hs-0.0.0.0 (constraint from user
target requires ==0.5.0.0)
Dependency tree exhaustively searched.