On Sun, Mar 1, 2015 at 6:45 AM, Alexander Genaud <alex@genaud.net> wrote:
# cabal install xmonad-contrib
Resolving dependencies...
Configuring X11-1.6.1.2...
...etc...
checking X11/extensions/Xinerama.h usability... no
checking X11/extensions/Xinerama.h presence... no
checking for X11/extensions/Xinerama.h... no
WARNING: Xinerama headers not found. Building without Xinerama support
checking X11/extensions/Xrandr.h usability... no
checking X11/extensions/Xrandr.h presence... no
checking for X11/extensions/Xrandr.h... no
configure: error: X11/extensions/Xrandr.h (from libXrandr) is required
Failed to install X11-1.6.1.2
cabal: Error: some packages failed to install:
X11-1.6.1.2 failed during the configure step. The exception was:
ExitFailure 1

You will need the development version of that library installed. In Debian-alikes, the development versions of library packages have names ending with -dev.

~d