Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: gi-gtk (user goal)
rejecting: gi-gtk-3.0.6, gi-gtk-3.0.5, gi-gtk-3.0.4, gi-gtk-3.0.3,
gi-gtk-3.0.2, gi-gtk-3.0.1, gi-gtk-0.3.18.15, gi-gtk-0.3.18.14,
gi-gtk-0.3.18.13, gi-gtk-0.3.18.12, gi-gtk-0.3.16.12, gi-gtk-0.3.18.10,
gi-gtk-0.3.16.11, gi-gtk-0.3.16.10, gi-gtk-0.3.16.9 (constraint from user
target requires ==0.3.16.8)
rejecting: gi-gtk-0.3.16.8 (conflict: requires pkg-config package
gtk+-3.0>=3.16, not found in the pkg-config database)
Dependency tree exhaustively searched.