I don't understand the error because it appears to be requiring a version of the same package that I'm trying to install.
$ cabal install gtk-mac-integration
Resolving dependencies...
[1 of 2] Compiling SetupWrapper ( /var/folders/cU/cUDMo9+9Gl817+j+h1DAvk+++TI/-Tmp-/gtk-mac-integration-0.1.0.46479/gtk-mac-integration-0.1.0.4/SetupWrapper.hs, /var/folders/cU/cUDMo9+9Gl817+j+h1DAvk+++TI/-Tmp-/gtk-mac-integration-0.1.0.46479/gtk-mac-integration-0.1.0.4/dist/setup/SetupWrapper.o )
[2 of 2] Compiling Main ( /var/folders/cU/cUDMo9+9Gl817+j+h1DAvk+++TI/-Tmp-/gtk-mac-integration-0.1.0.46479/gtk-mac-integration-0.1.0.4/Setup.hs, /var/folders/cU/cUDMo9+9Gl817+j+h1DAvk+++TI/-Tmp-/gtk-mac-integration-0.1.0.46479/gtk-mac-integration-0.1.0.4/dist/setup/Main.o )
Linking /var/folders/cU/cUDMo9+9Gl817+j+h1DAvk+++TI/-Tmp-/gtk-mac-integration-0.1.0.46479/gtk-mac-integration-0.1.0.4/dist/setup/setup ...
[1 of 2] Compiling Gtk2HsSetup ( Gtk2HsSetup.hs, dist/setup-wrapper/Gtk2HsSetup.o )
[2 of 2] Compiling Main ( SetupMain.hs, dist/setup-wrapper/Main.o )
Linking dist/setup-wrapper/setup ...
Configuring gtk-mac-integration-0.1.0.4...
setup: The pkg-config package gtk-mac-integration version >=0.9.6 is required
but it could not be found.
cabal: Error: some packages failed to install:
gtk-mac-integration-0.1.0.4 failed during the configure step. The exception
was:
ExitFailure 1
It doesn't want the Haskell package gtk-mac-integration, it wants the system package gtk-mac-integration. That is, the Haskell package you're trying to install is just a binding to the gtk-mac-integration library (which I think is bundled with GTK+); you'll have to install it separately before you can install the Haskell package.
If you already have GTK+ installed, then the problem is that the pkg-config tool Cabal uses to find external library dependencies can't find the corresponding .pc files for the library. I don't know how to fix that, though; at least not without more details.