optional_depends vala \
                 "--enable-vala=yes" \
                 "--enable-vala=no" \
                 "for vala support" \
                 "n"
                 
optional_depends gobject-introspection \
                 "--enable-introspection=yes" \
                 "--enable-introspection=no" \
                 "for object introspection" \
                 "y"
